So first, try to use UML diagrams. Both the class diagram and the seq diagram. I.e. you should start writing code only after you have the full design in detail

So first, try to use UML diagrams. Both the class diagram and the seq diagram. I.e. you should start writing code only after you have the full design in details. In short, think of yourself as a human code generator. The issue with programming is that you need to hold both the 3000 level picture and the 0.1 level, so working with diagrams should help. The second thing to think about state machine, especially one that are specified by tables. Before you write the code, make a table of each input state, and map it to your program output state. This would make sure that you did not forget anything. Look at the work of David Parnas in this area.