Don't write tests to get full coverage of your code. Write tests that guarantee your requirements. You may discover codepaths that are unnecessary. Conversely, if they are necessary, they are there to fulfill some kind of requirement; find it what it is and test the requirement (not the path).
Keep your tests small: one test per requirement.
Later, when you need to make a change (or write new code), try writing one test first. Just one. Then you'll have taken the first step in test-driven development.
