Demonstrate an aggressive attitude. Don't hesitate blocking a lineman or a linebacker on a running play. If your team is playing against an aggressive run defense, the ability of the tight end to block will go a long way toward determining the success of the running game. Whether you are assisting the offensive tackle with a 2 on 1 block of the defensive end or you have to take on an outside linebacker, a tight end must make that block as if the game depends on its success.
Understand your blocking angles. You will almost always be the second man in when blocking a defensive lineman. Even though you may be outweighed by 30-50 lbs when getting this assignment, you will be asked to demonstrate your toughness and upper body strength. You will also be asked to get him moving away from the play so that the ball carrier has more room to run or the quarterback has more time to pass. Do not let the defensive end man-handle you and toss you aside. That means you have to get in the first blow and stick to his chest until you hear the whistle. You'll likely get pummeled and beaten, but you can't let him toss you aside.
Vary your technique when blocking an outside linebacker. On a running play, the idea is to get between the ball carrier and the tackler and hold your position. Outside linebackers are among the most athletic and aggressive players on the field. Winning that battle will be very difficult over the long run. However, if you can get your body between him and the ball carrier and knock him off-stride momentarily that will provide enough of a crease for the running back to get through and make a big play.
Downfield blocking is a much more palatable assignment. This is what tight ends relish. Instead of being asked to take on a powerful defensive lineman or an athletic linebacker, the tight end has to get downfield and block a defensive back. This time the tight end has the weight and strength advantage. Once a tight end has the cornerback or safety in his sights, the block can usually be delivered effectively. However, defensive backs are quicker and can avoid the block if they are surveying the field as they are coached. It's hard to sneak up on a 190-lb safety, but that's just what a tight end has to do much of the time.
Sustain your blocks all the way through the whistle. Don't stop just because you have delivered the initial blow and the linebacker or defensive lineman has managed to get away. Get after your man again and do whatever you can to give the ball carrier (or receiver) the space to get out in the open.