It doesn't get more basic than 'Sit'. Every dog knows how to sit. All you have to do is put it on cue.
Relationship based dog training philosophy

Sitting Greyhound

1. Stand in front of your dog, facing him.

2. Put a bite-sized treat between your thumb and forefinger, and hold it just in front of his nose.

3. Say, "Sit" as you slowly move the treat up and over his head so that he tracks it with his eyes. (keep the treat low enough that he doesn't try to stand or jump to reach it)

4. As he follows the treat, he will naturally move into a Sit.

5. The instant his bottom touches the ground, say "YES!" and give him the treat.

6. Release him from the Sit with a release command, such as "Free dog!".

* If your dog gets up from the SIT before you release, guide them back into position but do not give another treat. In the beginning, only ask for a couple of seconds before releasing, and gradually work up to longer times.

Sit

Want to know more? Try Dog Training For Dummies by Jack & Wendy Volhard. Better yet, enroll your dog in an obedience class!