Things to cover can include first right of refusal to buy the other person out, shared expenses etc...In short, be careful not to rely on the goodwill between you and your friend.

That being said, it can save a lot of time and goodwill to explain to tenants fair procedures as long as they are trying to cooperate with you and genuinely don't understand.

Good will comes when it comes.

You want to keep good will with your tenants as long as possible.

Their ongoing support and goodwill is your compensation.Note also that none of these strategies requires you spend one penny from your pocket.

Pick up some cheap wireless routers from Goodwill for $5 and you’ll find most can already function at either end of that wireless bridge (either converting the existing municipal WiFi to Ethernet or rebroadcasting that Ethernet cable in a basic “bridge only” mode that gets you out having to do late night web search for “Double NAT” which is actually far more annoying than the physical bugs of the same name. 

I do this because I'm passing on the goodwill that was extended me, making the tenant more at ease about signing a long-term lease, and I firmly believe that more owner-occupied properties in our up-and-coming Buffalo neighborhoods is a good thing. 

You spent some time with him, so maybe have some goodwill there..

Because they insisted, I lowered my first month's rent as a gesture of goodwill but I feel like I've been cheated just because they are being stubborn. 

Small price for good will and a good neighbor.