If you have heavy duty card stock or pressboard folders, that is a good material to make a mock up out of and when you're down you have your pattern. Because of the durability of the material you can lay out your stich and pocket lines and erase if necessary. Heck, you can even sew on it to see what your spacing and thread size will look like. I do this because I still haven't found a leather eraser, so doing it on paper first saves me from ruining leather and feeding my scrap box. I know some use regular paper, tracing paper, etc. but those won't leave you with a durable pattern for future use.
BTW, for me, I seem to spend a lot of time on design and layout the first time I make an original item, so once I have a good pattern, I make notes on it and file it away for future use.
Hope this helps and good luck, like some of the pros on this forum say, just keep trying new things, be creative, and keep it enjoyable.