The 3/2 plan is a bet on both bets at once. Three chips are placed on Red, Black, Odd or Even, and two chips are placed on one of the three columns. The theory is that enough numbers are covered in one spin to give the player a chance to make a profit.
The best roulette strategy requires you to change the size of the bet based on your results. For example, when using the Martingale strategy, you have to double the bet after a loss and then reset to the initial bet after you win.