I recently stumbled upon this graphic (courtesy of josuedric.com) that I think is relevant to all freelancers:

5  things every designer should know when dealing with clients

 

I would just add an extra tip to number 2:

 If you do decide to give a client a discount make sure you have that written on your invoice. So if they recommend you to others your full pricing is clearly stated and you won’t get stuck in a cycle of discounts.

 

Any tips you would add?