The only strategy is knowing when to quit.
Be fast to place your bets and try to put your money in the squares that have the highest chances of winning (Red or Black, Odd or Even, 1st half of 2nd half, 1at 12 or 2nd 12 or 3rd 12)

Here my favorite roulette trick. After 80-100 spins from beginning of the game 6 spins are not hitted yet. And i bet on them from hit to hit until 2-3 spins are still not hitted, then exit. This trick always gave me profit.
To watch over game statistics i use free roulette statistics analysis tool Roulette Analyzer http://www.onlinecasinolist.info/roulette/analyzer.htm

Many people think there is little to discuss when it comes to roulette strategy. This may be a bit of truth and a bit of untruth; the fact of the matter is, roulette strategy is simple but subtle. Overall the math behind roulette is simple, but not very friendly. American roulette has a house edge of 5.26% for every bet except one. What’s worse is the other bet (five-number bet) give an even worse house edge of 7.29%. What it comes down to if you want to utilize a roulette strategy that’s effective, is looking for extended rules.

Atlantic city casinos for the most part entertain a beneficial rule. If this rule is in place (ask at the table before you play) you’re as close as you’re going to get to using a roulette strategy.

The rule applies only to outside bets that pay even money. Those are: red/black, even/odd, and high/low. If the ball lands on 0 or 00 (double zero) you only lose half of your bet instead of all of it. The casinos edge then drops to about 2.63%, still not in your favor, but a heck of a lot better.

The numbers looks like this:

Advantage = [18/38 x 1] + [18/38 x (-1)] + [2/38 x (-0.5)]
= -1/38
= -0.0263
or a house edge of 2.63%

Another roulette strategy to employ is keeping an eye peeled for wheels that don’t have a double zero. European roulette wheels come this way standard, but American tables rarely use it, as it decreases the house edge. Over 12 bets the house edge drops to 2.7% so keeping an eye out for this is a smart roulette strategy and good luck to you.