What it all boils down into is what you final goal truly is. Do you simply wish to finish the game? Do you want to collect all the trophies? Do you intend to get a really high rank in the leader boards? Those going for a quick run will focus on earning cash, buying the best guns they can get and of course, speeding up the repair skill. This means finishing the game pretty early (around the 20th wave or even earlier) by focusing on repairing every free moment you can get –even in the middle of combat.
Going for all trophies will require you to save up enough cash to buy all the guns, deal out plenty of mine-kills and use the flamethrower to kill a set amount of targets. Not all that bad, considering that the most you will have to do is to hold off on fully repairing the car until you have gotten all the other achievements short of winning the game.
