I'm old school. Pen and paper. I often make sketches and then may refine it for the final drawing. I do this mostly for spindles and finials. I find that if I design it first, even roughly, the end product is usually better than if I design while turning. Hollow vessels are too dependant on the grain and figure in the wood to decide up front what shape it will be. I might start out with an idea but quite often I make subtle changes as I turn based on how the wood is showing itself. Of course I'm not computer literate and the drawing programs I tried were not intuitive to me at all.