I start with a rough sketch of the whole quilt.
Once I think that it will work, I moved to a more measured drawing (big picture) Graph paper works well for this..One squre = 1 inch or what ever scale you want to work with..
The purpose of this excercise is to make sure that everything will fit evenly..ie, Im using 12 inch blocks and 2 inch sashings,, will this equal the measurement I expect or do I need more blocks, bigger sashings, etc.
If you are going to do a central medalion,, draw that in first so you can fill in around it..
Once I get that done to my satisfaction, I move to real life drafting of the design/pattern.. If its a block, draft it out real size..
From that I get cutting sizes.. I write these right on my life size drawing..
Make a test block if you are not sure how it will turn out.. this is the time to make adjustments..
When you are happy with all of that..Estimate yardage...buy fabric... start sewing..
voila, you have a quilt