Dymo tape, flat steel (flexible) ruler, electricians tape, draftsmen eraser guides...etc.
Tools, well over the years I have found that no single tool is the answer...like a good ink pen you need to find the one that works best for the individual and fits comfortably in ones hand. I have also found that there are times when you need different tools to accomplish different tasks/effects. Some I purchase, some I fabricate myself.