1. DON'T LOOK DOWN
Looking down destroys your posture.
If you are in the correct technical position--hips back, belly forward, chest out--then he won't be able to both keep his guard closed and attack you with triangles, chokes and armbars.
If his guard does open, then scoop-leg or knee-down and pass to the side.
2A. STEP OUT WITH THE LEG
The step-out should be to about 5 o'clock, completed in one sudden move. Don't step out to 3 o'clock and then try and walk your leg back to 5 o'clock.
Practice reverse lunges to perfect move and maintaining of base.
Once you've completed the step-out, stop and make sure your base is solid before opening the guard. His best attack will be a sweep at this point.
2B. TURN YOUR BODY TO THE SIDE
Don't just turn your head to the side.
Turn your whole body perpendicular to the guy on the ground.
You want to be looking in the same direction as the knee you are working on.
3. KEEP YOUR POSTING ELBOW TIGHT
Your elbow must remain in contact with the thigh.
Keep your elbow against your side, as well.
The primary goal is to keep the hip in check. The secondary goal is to block the guy from coming up.
4. OPEN THE GUARD WITH THE "BACK OF YOUR BUTT"
What opens the guard is the pressure your hip blade puts on the crossed ankles of the closed guard.
Keeping a hand on the knee on that side and maintaining a good base, walk from from 5 o'clock around toward 6 o'clock and even farther if necessary, pressing your hip blade (the side of your hip, the "back of your butt") against the crossed ankles.
Be ready to pass the guard as soon as it opens. If the leg stays up, then scoop-leg. If the leg goes down, the knee-down.
Saulo Ribeiro Explains the Passing of the Guard on the Ground
