The guard is an essential survival tool of Gracie jiujitsu. The guard can generally be split into closed (where your ankles are crossed around the opponent 's torso) and open (where the ankles are uncrossed yet the opponent is not past the legs).
The number one goal from the guard, open or closed, is to keep you safe from knock out punches. Think about it, if someone can't punch your face they can't really control your spine. If they can't control your spine they can't properly pass your guard.
To allow the open guard to serve this goal, we need to abide by certain rules of jiujitsu / grappling. The following 6 rules are very clearly explained by Carlos Gracie jr black belt Mr Adem Redzovic from Chicago Jiujitsu. His 26minute video can seriously improve your guard game :
1. If you open your guard, you'll play open guard. If your guard is opened, you're being passed.
2. Always maintain 4 points of contact.
3. Your feet are your first line of defence. Use them against your opponent's pressure.
4. Your knees are your second line of defence. They can neutralise pressure.
5. Third line of defence: correct body position. Make the initiative to be first with your defensive positioning.
6. The reset. Get back to where you can work again.