I have a friend who gives me a lot of tips. Last year I backed a lot of them and seemed to do alright, although I have no idea if I was up or down over the season.
Just decided I will try and track it a bit better and thought it would be fun to keep it updated here.
My "system" is to judge how good the tip is for myself and back it. If it is low odds I will do 2 or 3 units, higher odds 1 unit maybe each way. Its that scientific!