Can somebody tell me how to ensure maximum code coverage and test coverage?
One way in which you can attain better results through testing is by incorporating automation into the test plan. There is no way that the complete testing process can be automated, so you have to come up with a plan. The plan should highlight test activities that have to be performed manually and via automation.
Coverage is a useful metric but its scope is limited. There is no ideal way in which you can measure the effectiveness of the efforts spent on testing. It is a known fact that 100% coverage is only a myth.
A holistic approach that encompasses different types of testing e.g. automation testing, integration testing, manual testing, cross-browser testing, etc. would be extremely useful. It helps you measure the effectiveness of different tests and test systems in a single place.