Payoffs in roulette are based on a wheel with 36 numbers, so if you make a straight up bet on the 7 and win, then the payoff is 35 to 1. Since there is a zero on the wheel, the odds change from a true odd of 36 to 1 to one which favors the house, which is the 35 to one bet. The European wheel gives a 2.7% advantage to the house, while the added double-zero on the American wheel gives the house a 5.26% advantage (except in the quint bet, which gives the house an almost 8% advantage. Since the zero and the double zero are both green, then they are losers on the Black and the Red bets. The only exception to this is where some casinos offer “surrender” or “en prison”. In this case, half of the amount of any Even Money Bet is returned to you if the zero (or double-zero) is the winning number. This significantly reduces the house advantage by almost half. Because of this, not many European casinos offer “surrender” since the house edge is so low to begin with. Check with the dealer though to find out if the casino does indeed offer surrender.
Serious roulette players usually prefer to play outside bets because even though the payouts are smaller, the probablility of winning is higher. All in all, the best way to improve your odds is to play on the European wheels, or single zero. This eliminates the very bad quint bet.
There are “urban legends” of the possibility of a “biased” wheel while playing roulette, in other words, a wheel that favors certain numbers. While there may be a biased wheel or two, the bias would have to be very great to overcome the house advantage. However, it is very unlikely that you will find a wheel with a bias since the wheels are made with such precision today. To be honest, the casinos have a vested interest in maintaining their mechanically-induced randomness.
The reality is that winning and losing in roulette often takes place in streaks. If you do happen to find a system that is working for a time, stay with it while it lasts and then get out as soon as it starts taking a turn for the worse. Remember, roulette is a game of chance, not skill. So, lay down your chips, sit back, and enjoy the leisurely pace of the spinning wheel.