The Martingale Strategy is arguably the best roulette strategy, and it's certainly one of the most famous ones. Simply put, you don't hold back when you lose; you do the opposite. Whenever you lose in roulette, the Martingale Strategy requires you to make your bet bigger than the previous one.
So you cannot make money consistently playing roulette, but you can make money occasionally when you defy the odds and have a lucky day. That is called variance, and it is what makes casino gambling fun and exciting provided you play within the limits of your budget.