Oh. I'm also still learning things, and one of the real skill based elements to this game seems to be intelligent use of money. Here's what I've been doing, and help me when I could improve.
I started with training. Everything I got up to level 25. Getting snorlax and powering up taught me the importance of putting love into food. 25 is cool. Leaving that alone for a long time. On to food. Everything to ten, then fifteen, and so on. As I level unlock new training I have to stop food, buy it, and work that new one up to 25 before I go back.
Sound good? I really like the sleepy, fat guy for two reasons. First, the random encounter. Second, he has the unique ability that he gets effectively better every time you power up food. Then the candy dumps and it becomes splitting the focus in power leveling.