There are lots of options. Use what works for you, keeping in mind that a good marking tool will give you a line you can see, that stays around for as long as you need it, and is completely removable when you're done with it.

Projects that are handled a lot need a marking tool with staying power, others might do well with a line that brushes off.

Whatever tool you use, TEST IT before you begin. Water (ph level, mineral content, additives) varies from town to town and over time. It can make a difference.

Bohin Refill "Leads"
My go-to marking tool. Extra fine line, water soluble - can be washed out or erased. Get a free mechanical pencil with each refill. Five colors, 6 ceramic "leads" in each container. (Click picture to read more, get link for free Pencil Pocket pattern.)
Sticky Template Plastic
Make accurate, sturdy templates in 3 easy steps: peel, stick, cut!