The first thing you should do is say thank you because these simple words mean a lot. it is the best way to express your gratitude. You can also do the things I shared below- 1. Cook something delicious and give them to your neighbor 2. Give a gift to them, select something simple or based on what they like. 3. Help them in some way that's the best way to thank them. 4. Invite them to dinner and have a nice conversation with them and tell them how grateful you are to them. 5. Have a BBQ party and invite your neighbors to it.