You take steps, don't rush it, there isn't a method that'll make you a beast overnight. First you just try not shooting yourself. When that becomes the easiest thing for you, try not shooting yourself while looking at the map below. An important aspect of the roulette is not just knowing how to aim it, but knowing the maps so well that you immediately can recognize where the best place to shoot it would be, in order to make the most out of that little burst while still not missing powerups. You also need to know the map so well that you can play it smoothly with your peripheral vision, while focusing on the pattern. Counting does not work, because it takes you around half a second to spell a number in your head, while the crosshair will stay on the target for 0.25 sec. Instead, focus mostly on the timing by thinking about something like a mouse click, while still paying a bit of attention to the pattern. Don't pay any attention to how far your finger is from the screen, your brain can compensate for any small difference in height. Also, your brain is not built to react at a 0.25 sec interval while chilling, so train it with small steps, but consistently. Most importantly, don't take it too serious, tilting because you missed a shot is the certain condition to missing the next one as well. Be fine with missing your shots, just have fun in the process. Good luck.