Renting out a room whilst still living in my house.?

I am looking to rent a room out to help me pay a crippling mortgage my ex has left me with. Can I find a template anywhere which can give me guidelines as to the terms and conditions for the lodger. I just know that I will leave out a heap of stuff that I will later regret. Another question would be, what should I charge? (a double bedroom in a semi in dunstable) thanks to any response.