I was trying to match all four initial corners and getting no where, then it finally clicked for me and I focused on the top left corner. Much easier, but still quite a challenge with the timer talking to me! Is a worthwhile 'protip' to use up all 3 bombs on each run?
You get a bomb each time you finish a level, so you have to get to at least level two before you can use a bomb.
I tend to use them when nothing is jumping out at me. Whatever color appears the most on the grid will be removed, making it a lot easier to see four tiles that will line up to create a rectangle.
I'm going to post a strategy thread on twitter this afternoon!