Code coverage is successfully used to guide white box test design and evaluate the respective test completeness. However, simple overall coverage ratios are often not precise enough to effectively help when a (regression) test suite needs to be reassessed and evolved after software change. We present an approach for test suite assessment and improvement that utilizes code coverage information, but on a more detailed level and adds further evaluation aspects derived from the coverage. The main use of the method is to aid various test suite evolution situations such as removal, refactoring and extension of test cases as a result of code change or test suite efficiency enhancement. We define various metrics to express different properties of test suites beyond simple code coverage ratios, and present the assessment and improvement process as an iterative application of different improvement goals and more specific sub-activities. The method is demonstrated by applying it to improve the tests of one of our experimental systems.