The best way to maximize your profits with skill gaming is to become a master of one or two game types. I personally play the brick/paddle/ball games the most, and a few of the classic arcade games, like Pac-man. What you want to do is practice and practice some more for free on which ever site you plan to deposit on first. Play for hours on end, as much as you can. Play for a week or two before risking a single penny.

By doing this you are going to be able to dominate the lower rankings of the site and guarantee a solid profit to start you off before you reach solid competition and take a loss here and there. If you joined one of the sites with larger tourneys, you should be able to finish top 10 of one of the tourneys in the lower ranks and at least double your deposit. 

When you finally reach the medium to high rankings, begin to play 1vs1 games. Play 3 games, if you face the same opponent and keep winning 2 outta 3, then continue to play until you face a new person that you don't beat. Picking different times of the day and days you play, you will find a bit weaker competition. 

Once you Turn €20 into €60 or more, withdraw your deposit (€20), and begin the process over.

Follow that process and you'll be able to turn a nice profit while still having plenty of sites to choose from, for when you decide to master a new game type and run the ranks for the new game.