Start with the initial bet of one chip and after every loss, double your bet. In case, you do not know any strategies or betting systems on roulette, try the easiest one - The Martingale. It has the same random number generator as the ones in the real money online casinos. Free roulettes work the same way as the real ones.
Do you have your favorite roulette strategy? Try free online roulette and test your system.