I use this system ONLY for CUP matches.
So here it goes: I choose a particluar Cup on which I focus all my attention. Last week I decided to choose the French Cup. I take 5 matches in which teams from the first league that don't have any interest in winning the cup really (and so will field their younger players) play against a lower team from the second or third division.
I pick out the best 5 games and then place my bet on the underdogs that probably have odds around 7.0 or even higher.
I bet £10 on each game and almost every time I get at least one winner if not more from those 5 games and so I get a profit of at least over £20 every cup leg.
This system is great, I hope you'll like it.