I'm one of the converted in terms of test-driven development. One of the main "aha" moments for me is not to write unit tests - it's writing testable code. Any code that's testable is sure to be of a higher quality and easier to maintain than typical spaghetti code.
That brings me to the second part of the title - mocks. The art of mocking objects have taken off over the last couple of years. However, I feel that there is a real danger of abusing them in order to test code, when the code is not written in a testable way. I've seen many examples where mocking is used in such abundance that what you're testing is the mock object's functionality - and not your code. In cases like these you'd be much better off refactoring than mocking dependencies.
So here's my recommendation : focus on writing testable code, and try to minimize the use of mocks. Only use it when you've got no other method of testing your code.