1) Always always ALWAYS find a snack your pet loves/likes, it will boost the exp (This is just overall help), and make getting that level up easier. I use crafted snacks to help me along.
2) Choose a path. I almost always start by heading to the bottom left corner, then up to the top left corner, then into the middle, back to the top left, into the top right, then into the top bottom, but this will change depending on ghost locations.
3) Avoid ghosts. They freeze you and take up time. I will always look ahead to see if the ghosts are coming at me, or if I will end up following one (withing range that I will catch up to it), and if I am, I change my path.
6) The red stars. The red stars will always be helpful. They increase your speed, and that means you can get more apples (or cake, or whatever) faster. You can still be frozen by a ghost though, so be careful. when you are under the power of a red star, rainbows shoot out from your pet.