Fastest gains in code coverage come by starting your tests at the highest level.
Look at what the application is doing, and write a test for each separate task.
For instance, in a human resources application you might write one test each for:
New hire
Fire employee
Generate payroll
Schedule vacation
Raise salary
Change address
etc.
Notice that none of these have anything to do with how the code is structured. They don't even care what language the program is written in.