[Yumyums Inmahtumtums]

A trick learned while working in the restaurant business.

Sear one side of the steak. Give it good grill marks. Don't overdo it.

Flip it over. This is he magic side. Use the juices that come up as an indicator of how the meat is cooking. Here are the stages the steak will go through indicating it's readiness.

Cooked for a little time, no blood has come through the seared layer yet = rare.
Blood starts to seep through - medium rare.
Blood has come through for a bit now - medium.
Blood is slowing down - medium well.
Blood stops - well done.

The only time it's failed was when I second guessed it.