some tricks and hints:
+ If you have hard time on hitting, buy area or missile weapon.
+ best amus(in my opinion) are heimdall, odin and loki
+mines might have big attack power, but they are useless.
+be sure to get excalibur before lvl 20. It helps lot in final level
+if you really wanna rack damage, buy multipath weapon and fly so close the enemy you dare.most attacks should hit, and then deal great damage.
+press w to switch to closest enemy. this increases change to hit moving enemies.
+up shields first. You can't win game with out shield ups.
+loki is able to be defeated without taking dmg, use fast ship
+best level to gain money is 19
aand easiest loki battle = excalibur,heimdall (yes the heimdall) and lots ups in shield. heimdall can easily survive until overdrive is ready, use it and you will be healed. excalibur will kill it easily. besides its the most powerful weapon (yes it is. 3 projesctiles x 550 is more than 2x600)