The quickest way to increase your score is to do flips, but these can throw your ship out of control if you can't recover control. To do a flip, hold one of the thrusters to spin your ship, and for each time that it goes around once, it'll count as a flip. You get a 2x bonus if you do two flips in a row, a 3x bonus if you do three in a row, and a 4x bonus if you do four in a row.