Blocking is all about having an attitude. YOU MUST MAKE BLOCKING PERSONAL. You're going against someone else who is trying to embarrass you in front of your family and the fans in the stands. WRs should not take blocking lightly. This is also important because great coaches will follow the motto of "No block, no rock." How fun is receiver if you don't get the ball. Here's a little secret too, if you're consistently blocking there's a good chance that your coach will call more plays to get YOU the ball.
The best thing any WR can do to get better at blocking is watching the amazing beasts that are offensive lineman. They do it every play. But here is how you should start:
Identify the person you need to block (Duh). But sometimes it'll change mid-play.
In a controlled matter, close the space between you and your defender. Don't sprint the whole way to them. Once you get within 4 yards or so break down and prepare your hands.
Once you're a yard away from them fire your hands into their chest plate and pull them into you. VERY IMPORTANT: If they pull away and you're not strong enough to hold them let go before it looks like you can get called for holding.
Keep your feet square and drive your feet until you hear the whistle blow.
TIP: Sometimes the best blocks as WRs is just getting in the way of a defender. Not every block needs to be a pancake (even though we'd love to see that).