It is a wonderful way to learn about history. There are some basic rules you should follow and some tools you need to get started. If you plan on doing rubbings of your family or relatives then some of these won't apply. I like to rub very old tombstones. They have a certain charm about them.
Many cemeteries are private property.
Be sure and ask before you start rubbing tombstones. Trespassing fines are not cheap. Treat each tombstone as if it were your own mother's. Somebody loves these people and old tombstones can be delicate. Make sure and clean off all marks accidently left on tombstones.