Being a lazy f***, I'll just pick out ten of the best (and most concise) from Heinlein's Notebooks of Lazarus Long. But there are far more than ten valid ones.

If you don't like yourself, you can't like other people.

Cheops' Law: Nothing ever gets built on schedule or within budget.

Your enemy is never a villain in his own eyes. Keep this in mind; it may offer a way to make him your friend. If not, you can kill him without hate -- and quickly.

One man's theology is another man's belly laugh.

Sin lies only in hurting other people unnecessarily. All other "sins" are invented nonsense. (Hurting yourself is not sinful -- just stupid.)

Any priest or shaman must be presumed guilty until proved innocent.

Be wary of strong drink. It can make you shoot at tax collectors -- and miss.

"Go to hell!" or other insult direct is all the answer a snoopy question rates. (Comment by Midchuck: This is actually unneccessarily verbose. Two words would work as well as three.)

Rub her feet.

A motion to adjourn is always in order.

Peter.