When inside guard:
DO control one hand on the chest and one on the belt/hip at all times unless you are attempting a pass. Keep your chest out
DO keep your knees spread as wide as possible and sit on your feet (not your toes) your weight centered and keep good posture while in their guard to avoid sweeps.
DO: when your opponent is attacking your arm as if to go for an armbar, once he grabs it, make your elbow touch the ground, he will not have your arm, trust me.