In the lab area, talk to #2 and receive the Paint Set from him and bring it to #36 in Tron's Room. If you are just starting the game you will not have that room yet. Then go to the Ruins and get the momento and also give that to #36 to get the other set of colors.
There is an easy way to collect money in the level where you must collect farm animals. Instead of rushing to collect the animals, kill off the bird-like robots. One way to do this is to shoot one from afar. When it rushes you, just strafe away from it. Then use your auto-lock to target it again and resume firing, and repeat if necessary. When you see the bird-bot appear, send your server bots to "collect" it. They will pick it up and throw it into the truck. This counts as an "other" thing collected .When sold, each bird gives you 500 zenny and they always return.
Go to the level where you have to find Diana's tear and keep battling all the Reverbots. Go back to the Gesselshaft, return, and keep collecting the zenny from when the Reverbots were killed. Note: When in that level you have to get the bazooka to knock down the cracked walls
In the bank robbing level, rob the animal hospital then blow it up. In there you will see something that looks like an statue. Grab it and you will get 20000 zenny!
On Mission 1 in the city,since your bound to find items, take the servbots whose brains you want boosted along with you because finding items will boost up their smartness(brains).
When you've given your favorite servbot the red head parts,(You get it from #9 in the gym after a few missions)speak to #17 in Tron's room. He will ask you to rest since you've been working really hard and you were getting tired. While you rest,your favorite servbot will go to the casino to try to win lots of zenny for you. You can play high and low, and bingo.