As you continue to grow in your understanding of the Greek language, you would do well to spend more time readings the following books than you do studying verbal aspect:
Silva’s book is a challenging read, but its also very important. Its the kind of book you should probably read at least twice to grasp it and then a third or fourth time to master it. But your understanding of semantics and Greek will have grown exponentially if you do – and your exegesis and translation will also drastically improve.
Nida and Louw’s book is an easier read, but also provides discussion not found elsewhere. They guide you by the hand and show you how they determined the meaning of words and wrote their definitions.
Read them both. And then read them again.