At the begining make some money, and make it quickly.
Keep an eye on the mission system for an idea of what to do next, but don't be led blindly by it. Some of the missions require an expensive upgrade to participate in, and it's better in the long run to slowly unlock new tools and weapons.
Once Buddy's eyes turn into crosses stop what you're doing you won't earn any more money until he's started returning to normal.
You'll know when he's back to full health when he starts moving around the screen and has a smile on his face again.
Tired of the current on-screen action!? Tap on the trashcan icon at the bottom right-hand corner of the screen, then quickly tap it again. Buddy will be rolled up, thrown in, then magically appear elsewhere, ready for whatever you have next for him.
If your Buddy needs a new face head into the Profile section of the main menu, then tap on the Polaroid picture of him. From here, you can select a picture from your camera roll, or take a new one with your device's camera, and have it appear over Buddy's face.