There is a bit of a guide for matched betting here:
The Gambling Times | Matched Betting - Profiting from "Freebets"
It might be usefull. There is 101 different types of promotional offer/freebet which all have different T&Cs so it is hard to explain quite how and why people bet as they do for each type. There is no real "right" or "wrong" though, as long as you never lose you wont be going far wrong. This explains a very basic bet once and get a freebet strategy, I expect you already know that, but thats the basics.