It depends on how close you need to be.
If you simply want to be sure you are lined up on TDC for things like installing the distributor, remove number one plug and turn the engine til air puffs out the hole...it will be very obvious. Then look at the timing marks and line them up if they need a little move movement.
If you want to be closer, stick a piece of welding rod, coat hanger, or other stiff wire in the plug hole as you rotate the crank. The wire will be pushed back out of the hole as the piston rises...when it hesitates, you are at TDC.
If you want to be precise, you can take an old spark plug, break the insulator out of the of plug and thread the inside of the plug base and screw a bolt thru the base from the top side so that you have an adjustable stop. This is what I use. Or, you can just by a tool that is made the same way, they are cheap.
