I will start off this post by saying that in the game of roulette there is no gauranteed strategy to win, ever. This is why the casinos love it. It is a game of pure luck. There are ways to reduce your chances of losing by covering as much of the board as possible but this will mean smaller winnings in return for a bigger loss.
One strategy I came across when I used to visit the casino and play virtual roulette online and in the bookmakers was the Martingale strategy. This strategy I found very interesting. Basically what the strategy involves is, betting an evens shot such as red/black, odd/even. Take your stake and bet it on these evens shots. If the bet doesnt come up simply double your stake. Keep doubling your stake until you get a winner and you will not have lost money.
Say you bet 20 on red and it won. Bet 20 on black in the next bet and if it wins you are 40 up now. Then start again with 20 and keep betting it if your bets lose until you could be betting 400 just to break even. Sooner or later you will get a winner at evens (Hopefully!)
The flaws in this system however is the fact that tables have a minimum and maximum bet allowance. This means that if you are really unlucky when trying it you may only get about 8 bad spins until you have bet the maximum stake allowed meaning you will lose A LOT. Especially in comparison to the small amounts of winnings.