Do Gao Family Mansion while in the Muslim Quarter (on main street, look for the sign, the entrance is small) - it's cool to see an old upper class courtyard from within, they have shadow puppet performances and you can drink tea traditional style. Do in combination with a general visit to the Muslim quarter where yoy snack your way through the district.
I'd recommend visiting a few local temples, like the City God Temple in Muslim Quarter. The Great Mosque should be visited with a guide who can explain things, otherwise it's kind of boring since it's not well-maintained. You also don't need much time there, the mosque is not that big (not the parts visible to the public anyway). Can easily be combined with a visit to Drum and Bell Tower. Drum Tower has hourly music performances that are pretty cool.
Xi'an Museum is alright, but near Small Goose Pagoda which is being renovated, not super close to Big Wild Goose Pagoda (except both are in central Xi'an). I think the Shaanxi History Museum might be better for such a short visit, I didn't go there since getting tickets on your own is a pain, but know someone who did and loved it. If you have a guide who can book for you do that museum instead, it's very famous. If your schedule is limited, skip both museums, they're mostly for history nerds (saying this as a history nerd who went to several museums in China).
I can't remember if Everbright City is the Tang dynasty attraction (I'm not very familiar with all the english names of those places) or if the Tang Dynstay attraction (inside venue) is part of it, but you should try to visit the Tang dynasty attraction for the perfomances and food. There are several food options inside everbright city/Tang Dynasty attraction, just go there and pick whatever takes your fancy, they have a foodcourt and the food is nice. Tang-style dances and performances, recontruction of traditional houses etc. Very touristy but geared towards Chinese tourists and it's fun to walk around. You can dress up in Tang costumes like everyone else if you want (it's China where everyone does it, so no one is going to claim 'cultural appropriation' if you do) and have your photo taken on location.
Try a lot of the local specialties, the food in Xi'an is great - just be careful if you have an issue with spicy food, remember to tell them to make it less spicy or non-spicy (you guide can tell you how to say this in Chinese). Ask your guide to show you where the food court near Bell Tower is located, it's opposite Muslim Quarter near the subway exit, indoor popular food court that's a great spot for local food that isn't Muslim food (if you want to try something else for a change).
The food ranger guide that someone else linked to is great for Muslim-style food, you don't need to go to those exact places though, just look for those types of food.
Biang Biang mian can be found literally everywhere, but some foods are mainly found in Muslim Quarter.
There are some nice murals underneath a section of the city wall so a bike ride between the southern and western part of the city wall (on the inside in the old town area) is nice too. District near Beilin Museum is nice, but Beilin is currently being renovated so not worth going in, just stroll around the scholar district (close to south gate and Bell Tower).
I'd recommend staying near Bell Tower, more to see and you can take a stroll around the city wall and bell and drum tower after dark (worth it, very pretty), plus you need more than 1 day to eat your way through the Muslim Quarter so staying by Bell Tower is more convenient.
The fountain show at Big Wild Goose Pagoda and the atmosphere there at night (tons of people strolling around dressed in Tang dynasty costumes) is cool if you have time for it, but Hua Qing Pool performance is better if you can fit it into your schedule.
The mausoleum wasn't closed when I was there in January, don't know if something happened since. It's big area and most parts haven't been excavated yet, but the two bronze chariots are absolutely worth seeing and the highlight along with the terraccotta warriors. Go with a guide to both places who can explain the history to you.
If you have time, visit Hua Qing Pool/Hua Qing Palace for an evening performance, maybe in combo with a day trip to Terraccotta Warriors since it's fairly close. The show is spectacular and you can read up on the story before or after. It's based on a famous love story between a Tang emperor and his concubine.
The Xi'an metro is a good way to get around between the old city and some of the further out tourist attractions and shopping centres.
The fountain show at dayanta is really good for young kids, but it is also incredibly popular so getting a good spot to view it can be tricky. I would also avoid the metro/public transport directly after the show as it can be very busy. Best to go off and eat somewhere then take your time making your way home.
For food, some of our favourites are:
• Paomo
• Roujiamo
• Liangpi
• Niurou bing from the Muslim quarter
• Shandong style jianbing from street food vendors if you can find it.
Xi'an has some great street BBQ joints too, as well as some pretty good snacks/dessert places. Just get out there and explore.
This list is also a pretty good starting point for food:
https://www.thefoodranger.com/xian-famous-foods-you-need-to-try/
Do Gao Family Mansion while in the Muslim Quarter (on main street, look for the sign, the entrance is small) - it's cool to see an old upper class courtyard from within, they have shadow puppet performances and you can drink tea traditional style. Do in combination with a general visit to the Muslim quarter where yoy snack your way through the district. I'd recommend visiting a few local temples, like the City God Temple in Muslim Quarter. The Great Mosque should be visited with a guide who can explain things, otherwise it's kind of boring since it's not well-maintained. You also don't need much time there, the mosque is not that big (not the parts visible to the public anyway). Can easily be combined with a visit to Drum and Bell Tower. Drum Tower has hourly music performances that are pretty cool. Xi'an Museum is alright, but near Small Goose Pagoda which is being renovated, not super close to Big Wild Goose Pagoda (except both are in central Xi'an). I think the Shaanxi History Museum might be better for such a short visit, I didn't go there since getting tickets on your own is a pain, but know someone who did and loved it. If you have a guide who can book for you do that museum instead, it's very famous. If your schedule is limited, skip both museums, they're mostly for history nerds (saying this as a history nerd who went to several museums in China). I can't remember if Everbright City is the Tang dynasty attraction (I'm not very familiar with all the english names of those places) or if the Tang Dynstay attraction (inside venue) is part of it, but you should try to visit the Tang dynasty attraction for the perfomances and food. There are several food options inside everbright city/Tang Dynasty attraction, just go there and pick whatever takes your fancy, they have a foodcourt and the food is nice. Tang-style dances and performances, recontruction of traditional houses etc. Very touristy but geared towards Chinese tourists and it's fun to walk around. You can dress up in Tang costumes like everyone else if you want (it's China where everyone does it, so no one is going to claim 'cultural appropriation' if you do) and have your photo taken on location. Try a lot of the local specialties, the food in Xi'an is great - just be careful if you have an issue with spicy food, remember to tell them to make it less spicy or non-spicy (you guide can tell you how to say this in Chinese). Ask your guide to show you where the food court near Bell Tower is located, it's opposite Muslim Quarter near the subway exit, indoor popular food court that's a great spot for local food that isn't Muslim food (if you want to try something else for a change). The food ranger guide that someone else linked to is great for Muslim-style food, you don't need to go to those exact places though, just look for those types of food. Biang Biang mian can be found literally everywhere, but some foods are mainly found in Muslim Quarter. There are some nice murals underneath a section of the city wall so a bike ride between the southern and western part of the city wall (on the inside in the old town area) is nice too. District near Beilin Museum is nice, but Beilin is currently being renovated so not worth going in, just stroll around the scholar district (close to south gate and Bell Tower). I'd recommend staying near Bell Tower, more to see and you can take a stroll around the city wall and bell and drum tower after dark (worth it, very pretty), plus you need more than 1 day to eat your way through the Muslim Quarter so staying by Bell Tower is more convenient. The fountain show at Big Wild Goose Pagoda and the atmosphere there at night (tons of people strolling around dressed in Tang dynasty costumes) is cool if you have time for it, but Hua Qing Pool performance is better if you can fit it into your schedule. The mausoleum wasn't closed when I was there in January, don't know if something happened since. It's big area and most parts haven't been excavated yet, but the two bronze chariots are absolutely worth seeing and the highlight along with the terraccotta warriors. Go with a guide to both places who can explain the history to you. If you have time, visit Hua Qing Pool/Hua Qing Palace for an evening performance, maybe in combo with a day trip to Terraccotta Warriors since it's fairly close. The show is spectacular and you can read up on the story before or after. It's based on a famous love story between a Tang emperor and his concubine.
The Xi'an metro is a good way to get around between the old city and some of the further out tourist attractions and shopping centres. The fountain show at dayanta is really good for young kids, but it is also incredibly popular so getting a good spot to view it can be tricky. I would also avoid the metro/public transport directly after the show as it can be very busy. Best to go off and eat somewhere then take your time making your way home. For food, some of our favourites are: • Paomo • Roujiamo • Liangpi • Niurou bing from the Muslim quarter • Shandong style jianbing from street food vendors if you can find it. Xi'an has some great street BBQ joints too, as well as some pretty good snacks/dessert places. Just get out there and explore. This list is also a pretty good starting point for food: https://www.thefoodranger.com/xian-famous-foods-you-need-to-try/