The level increase when you've removed a certain number of blocks. The speed increases for every level. The score you get for removing blocks is calculated based on how many blocks you remove at the same time. So a good strategy is to make sure you remove as many blocks as possible at every time.

Hello, really nice game!!! Had me addicted right away. The only problem I had with it was when I reached 10000 points because I could not make the game end. Even if I had my dot right over one of the moving objects the game would not end (and I wouldn't get that Highscore I longed for  ). Great game though!!  

btw. I tried to attach a picture but didn't know how to do it.