Pretty simple. Talk to them when they come in. Show some interest. Get to know them.
2) Do show respect
Kids want to be treated like an adult, this is one area in which that works.
3) Do provide food
Food always works. Feed them. Even let them have access to the kitchen.
4) Do be fun
Do something unexpected from the normal routine. Be a little playful.
5) Do avoid confrontations
This isn't the time to correct your kid. Do that later, where you can discuss.
6) Do remember them
Names, siblings, & unique things about them. Also, how your kid knows them.
7) Do make it peaceful
An environment that's void of contention makes a place people want to be.
8) Do leave a little space
Give them some room. Not the bedroom. But, some talking space to be private.
9) Do like them
Everyone has annoyances. Overlook them. See what your kid sees. Be open.
10) Do keep long hours
It doesn't have to be 'open all night' but kids like late nights. Especially weekends.
Everyone wants to belong. Somewhere. Make it you and yours that they think of as 'family' when they need to connect. How you interaction with your kid's friends, and your kid, will benefit everyone.