Lord_Quortez
there are many many ways to do what you are asking. i can give you one tip. keep your center of gravity low. it makes it harder to move you. but for the best help i recomend looking into brazillian jujitsu. its a gerat grappling art that ive haad some experiance in. its a very simple style but it does aid alot in grappling.
Brazillian Jujitsu is the best, im a hefty guy and ill tell you speed is your best weapon. keep moving, wear him out, and dont worry if hes bigger than you, grappleing is like a chess game, wait for it long enough and he will make a mistake and hand you the victory.