There will be a few types of power ups in the game which will help you in situations where you are having a hard time passing the stage and reaching that level requirements. When that happens, you shouldn't forget that there are two types of power ups in the game: the ones which you choose right before you start the level (also can call them boosts), and the ones which you can find within the level.

I suggest that you use the boosts only if you've already played that level before and know that it is kinda difficult to finish it without an extra helping hand from the boosts (which should help give you a good head start). As for the power ups which you can find within the level, you should use them in case you have about 1 move left and 2 things to obtain towards level objectives.

Basically these power ups are there to help you in case you are stuck, so let me give you my advice:

Use the power ups at higher and more difficult levels, don't waste them at the beginning because you will have a much better use for them later when you get stuck.

Don't use the power ups or boosts while you have infinite lives because even if you fail the level, you can re-try for free - for sure you will pass it eventually.

Try to think ahead before activating the boosts and power ups, because the more you progress, the more you might need them - so don't waste them!