keep a bit of tape rolled on the end of your favorite pencil - this way you will always have some handy!
Masking tape comes in different widths - from very narrow stripes to very wide ones.
I usually find that a 1/2 inch wide stripe suits all my animation needs.
For marking tracks and paths you might want the wide variety - more room to draw on, write frame numbers and such.
Pencil doesn't write very well on regular tape, it rubs off and dissapears. Use a permanent ink pen if you want to be sure the marks will stay. Avoid water based ink - the whole point (the original purpose) of the masking tape is to resist paint!
Another extremely useful kind of tape is the removable and re-arrange-able type:
I love the Scotch Removable Tape:
Use this on the drawings themselves without damaging the paper or the artwork.
You CAN DRAW on this tape with pencil and pen!
Use it for fixing things that are on frame - the edges are usually invisible when scanned, or at least, rather easy to fix with Photoshop.
Do NOT leave the tape on anything for more than a few days.
It hardens, yellows, and can become impossible to remove after a time. This includes glass surfaces - be kind to your scanner!! After a month, the only thing that will remove it is a sharp knife...
I'm sure that as you work, you'll find lot's of other useful thing to do with this amazing invention.
Masking tape RULES!! ;-)
More Tools - see these free downloads: