Make them food and take it to them. Invite them over for a bbq. I found that the best way to make friend is be friendly. Strike up a conversation and let them do most of the talking. People love when others are interesting in something that interests them and they get to walk about it.
Go ask to borrow something they will have. Everyone likes feeling helpful
Make some baked goods or bread and drop it off. I like to use the excuse of “I accidently made too much, would you like these?”
Invite them over. Have dinner, drinks, hang out, do stuff you like to do with them. Watch sports, or a movie. Listen to music. Grilling is a good outdoor excuse to wave them over.
But keep in mind, proximity doesn’t necessarily make for good friends. You might not enjoy the same hobbies or foods or whatever. You may not enjoy each other’s company. Worse still, you might have different feelings about hanging out than they do. Are they close enough that you’d feel obligated to invited them to everything?
It’s best to invite them over a few times, but maintain boundaries.
not a dad, but someone co-living in an apartment with 7 other people
took me over a year of being a shut-in to start talking with them, and after a few months of connecting, told em i was a shut-in, but am now glad that i started talking with them, and they just accepted and respected it and that’s all
people don’t care why you haven’t initiated contact for a year, 3 years or a decade of being neighbors, all they really care about is the first “sup, hi” and how it goes from there
so, just, greet them and when you see they have time start a conversation. the rest will follow.