Well, in gambling and sports betting, first you need to make sure that the site is 100% legit and also the site is fair and trusted. Since you checked Roobet, it is a well-reputed site so you do not have any issues with that site.
However, winning in bets is something else and you need to be lucky in order to win the bets. There will be times when you will mostly lose most of the bets and during this period it is better to take a break from gambling. However at other times you may be having good luck and winning most of the bets.
You need to be lucky offcourse but everybody needs to find out for himself in what sports you have a good knowledge to place value bets. Don't just blindly place bets on a match (or on cards/corners), do your research before that. If you follow sports closely, you can find some value bets especially in the smaller sports (snooker, darts, ...).