There are two systems to Roulette strategy: Martingale System and the d'Alembert System
The Martingale System
The Martingale System only works if you are playing with no limit on your bankroll. The system is this: When you win a bet, you take the money off the table. When you lose a bet, you bet again but at double the amount, so that you win back the money you lost plus make a profit. The problem is if you lose again, you need to double that bet, and so on.
The d'Alembert System
The d'Alembert System supposes that the odds of a player winning decrease after a win, and the same with loosing. Thus the player should remove a chip from the bet after a win, and add one after a loss, to compensate. The problem with the d'Alembert system is that mathematically there is no “memory” in a gambling system – it is the same with every fresh spin.
These two systems do not have any way to change the odds of winning or the house edge, so they can’t possibly help you win at Roulette.