Most affirmative tú commands are just the present third person conjugation (just a hint). Some are irregular and just a matter of memorization.
1. Estudia
2. Come
3. Sé
4. Haz
5. Di
A funny way my Spanish teacher told me to memorize the irregulars:
Vin Diesel has ten weapons, eh?
With a German accent...
Ven (venir) di (decir) sal (salir) haz (hacer) ten (tener) ve (ir) pon (poner) sé (ser)