I haven't coded in java for a long time, and after coding in C, I'm having issued organizing my code for OOP. More specifically I'm not sure when to create a new method, and when to create a new class, and when to just lump everything together.
Are there some general rules or guidelines on how it should be done?
Take a look at the SOLID principles.
EDIT (some more pointers):
You need a SOLID GRASP of some design principles.
To start small, take a look at these first:
When writing code, high maintainability should be your ultimate goal, and it's all about assigning responsibilities and separation of concerns.
Well designed objects are SOLID.
This is a difficult question, one that everyone who worries about design has to figure out. I think it's the hardest part of using objects, light years beyond mere syntax.
Is is something that you think of as a thing, entity or actor in your system. Well then it's an object so make a class to represent it. There's no need to make it more difficult than it is.
First of all, never just lump everything together. Try to identify the objects first. Build a class for each object your program will work with. If you're building an application for truck drivers, you will need a class for the driver, the truck, the load he's hauling, there's really no limit to how far you can break these bigger objects down. As for the methods, a method handles an action for the object. Truck.Start() would start the truck. Drive() would start it driving, etc... Maybe the Drive method takes a Route object for an argument which contains the roads to drive on. In short, create a method when an object needs to do something and create a class when you want to deal with another type of object.