What to look for when being a landlord?

I've recently bought a 2 bed house and am looking to rent the spare room out and I will be a living landlord I guess. Just asking for advice on what I need to do and look for (legal wise) before doing so? It's tax free up 7k a year for renting a room out I believe. I used to live in shared houses years ago and vaguely remember being sent a sort of agreement before moving etc and a deposit too? How would I write an agreement/contract so I can send it to a tenant before they arrive? Any advice would be helpful thank you