Numblast

First start on Easy until Lv. 30, it will not be too hard but it will give you time to get the hang of the game. Use the snake combo method from Count Pork, practice and try to find your own style. By the time you start on Lv. 30 on Normal it will be much easier. Determination and concentration is needed here.

For Hard mode, practice, practice, practice! That is the only thing I can say, go for it and you will get it. It's not impossible, but it's very hard.