When we are on our feet, we employ a very simple philosophy: When in open position, with no contact, we should be positioned so the opponent can't get to our feet. Then, when they put their hands on us, we are in good shape because we hand-fight so well. We will concentrate on the open position for now.
Your stance is your first line of defense: keep your knees bent and your hips underneath you. Your chest is facing the mat, and your head is facing into your opponent. Head position is very important here - good head position allows you to use your noggin like another arm. Next, your elbows are down. Elbows are a big key to controlling opponents -we want to control theirs and protect ours. Whichever your lead leg is (and I know, with some wrestlers, it varies), the same-side arm has to defend shots. Keep that one low and reach less with it.
When the opponent attacks, you want to 'down-block'. That means dropping your attack-side arm to block, and stepping your leg back while dropping the hip onto them.
If done right, you can shut down your opponent's outside shots using your positioning and down-blocking techniques - whether or not that opponent is quicker or stronger than you.