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I'm assuming you mean sparring techniques.

With taller opponents, you have to be more mobile and faster than your opponent since you can't play them on the outside. One trick is to get on inside their normal kicking range (i.e. closer than they can kick you with a fast kick or round kick effectively) and start firing rapid round kicks (for example). You must also be able to get out before they can counter with punches or a crescent kick to your head (which would be really easy if they are that much taller than you).

Good footwork is a key component that many people overlook. practice shifts, singe steps, and double steps alone and in combinations. For example, you could single step forward, shift back, and double step forward. You can do this at home or during down time at the dojo. One of my favorite moves is a lunge. Many TKD fighters want to live off their kicks and are uncomfortable inside. You want the other guy to be uncomfortable, so I use the lunge and the threat of a lunge to take other people outside their comfort zone.

A lunge is a lightning fast thrust forward. The secret to a good lunge is that most fighters watch your front foot as a way to determine distance. At some point during the match, I slide my rear foot up close to the back of my front foot, then shoot the front foot out to an extended L as I execute a technique like a reverse vertical punch.

Finally, work in all directions, not just forwards and back. I like to work outside the other guy's attacking side. If he leads with his right, step out at a 45 degree angle left, block him inside, closing him up and giving you a rib shot as you angle by. This is a slashing attack and confuses many fighters, who are used to a more linear fighting style.

If you mean sparring I can advise the following. Similar to boxing. Keep moving. Always move to the side never back. Keep forward energy toward your opponent. Use combinations no less than three moves.

Without watching you spar that is the best i can do.

first is kicks. tae kwon do easily has the best kicks of any style, mainly because that's their main focus. but this can also be a weakness. tae kwon do's biggest weakness is close quarters, within punching range. move in and jam their kicks, sweep the foot before it is set down, any time they jump push them. any spin and bump their back, this will disrupt them enough to hit them. when a kick comes in block it but then raise the kick up, not enough to hurt them, but enough to hurt their balance. next is combos. a round kick that comes off of a front kick chamber can hit them before they know it. any time they punch exploit the opening to the ribs with a round kick or diagnol kick. if your point/tourny fighting, then when the do front kick or round kick you do spinning back kick (not for street) this will prevent theirs from getting in while exploring their opening.

hands. once you move in to punching range, grab their front arm pull down and strike. any time they punch you should block with minimal effort while putting most of your effort into the punch (watch wing chun for further explanation). clear the arm to give you the opening. push against their lead arm to keep it occupied and to open a shot to the ribs. explore the line of sight and how to block it using their arms.

against big guys you can't play the distance game you will lose every time, they can cover it easier. you need to move in and remove that factor.

enjoy and good luck. let me know if you have any questions.