Try this for breaking his closed guard:
1.Establish your Base and Posture, (Base -makes it difficult for your opponent to off balance your body,Posture-makes it difficult for your opponent to effectively apply sweeps and submissions.)
There are different kind of postures that you can do:
a)Example is Posturing up: by looking straight ahead,and swaying your back,(it will make your opponent harder to pull your head down)
b)An example of different postures that you can do with your hands(stagger your hands,hands on his bicep, hands on his armpits etc.),try not to put your hands on the mat ,that is asking for submission
,and if possible always put your hands in front of your head( so he can not sweep you)
c)Spread your knees apart as wide as possible , sit on your ankles and keep your weight and butt down(for base).
Your purpose is to keep his back flat on the ground and not to break your posture.
2.Uncross the opponents ankles/control the legs
an example of uncrossing his ankles(if he is in a closed guard)
a)your arm in his armpits or on his biceps
b)stand up ,still holding him down with your arms;
slightly turn left and put your right leg inbetween his buttcheeks;
c)kneel down (base down) - your knee should come in between his cheeks and your chest.
You will end up with your left knee on the mat and your sitting on your left ankle, your right foot on the mat with your right knee pointing up.
d) Spread your knees apart as wide as possible.( Point your right knee towards the center of your opponent's body,Point your left knee to your left (away from his body).
e) Tuck your elbows into the side of your body,hunchback and turtle your neck(to avoid submissions).
f). Keep your weight and your butt down.
g). Keep your right knee and thigh between his legs.
That should open his guard.
3.Secure and control your opponents hips
Keep him flat on his back ,do not give him any space so he can not move his hips.
4.Lock in upper body(go for cross face and dig in for underhook)
5.Pass under his legs(by doing, double under hook pass, leg on shoulder pass or any variation of this kind of passes) or over a leg(usually i pass on whatever leg he put down, or i can force one of his leg down then pass over it)
I hope this help.