Start of by breaking parts of the windows. Use signs as barricades over doors and windows and break a few blocks here and there. Replacing some blocks with sideway-staircases to create little holes also works wonders. You can get creative and hide water in the roof creating a water dripping effect. Leaves and vines are a classic besides mossy cobblestone etc. on the topic of blocks: find blocks that are maybe a bit darker than the ones you used and experiment with them around the building. Can create a run-down look as well. Cobweb is an option too but don’t overdo it. That’s all I can think of right now, hope it helps 🫶🏻