When you first look at a design, you have what we call Design Inertia (unless you are making it up from your own ideas). This is the initial period when you start to look at the drawings, etc., before you decide how to build the model. Obviously this takes time, dependent on your own experience and the quality of the information you receive. Some planning will be required, but sometimes the best way to tackle this problem is to start to create the model with the understanding that you will have to go back and make changes. Starting with the bits of the model that are easiest is an obvious strategy, and by the time you get to the more difficult bits you at least have some context to work with. Radical revisions of a model should perhaps be saved as a new project then you can always go back a step.
