Well, first things first. Get familiar with the berries. Sounds stupid, I know, but wouldnt you hate it if you chose a sniddberry over an aquaberry? (To see what I mean, look at the table below.) Before you study and your brain explodes, let me just say that I personally dont have the exact numbers memorized. The only thing you really need to know is which berry is better in relation to another. Isnt that simpler than all the numbers?
Below is the guide for the easy berries, and pictures. Just substitute the values for the medium and hard levels.