Toss the ball up into the air, using both hands so that it is spiraling. This will simulate how the quarterback will (hopefully) throw you the ball.
Pump your arms vigorously as you practice how to catch the ball alone. With the ball in the air, this will simulate you running without the ball. Then look up as you feel the ball is starting to descend.
Create a window with your hands. This refers to aligning your thumbs so that they are just about touching horizontally. The openness of your hands and the positioning of your thumbs makes it look like you have created a window. Place your window in the direction of the incoming ball. In this case, it's above your head.
Attack the football with your hands. Great receivers do not wait for the ball to come to them, they go to the ball. You never want to give the defense more time to knock the ball away or even worse, intercept the football. By going to the ball, you are reducing the time they have to react.
Catch and secure the football in your hands. As you make contact with the football, immediately rip it down from the sky and cradle it between your body, bicep, forearm and hand. If you imagine that you'll be running right through the defense, use the two-handed grip where one hand is on top and the other beneath the football.
Repeat this drill 100 times. If you do this drill 100 times a day, you'll develop some of the quickest hands on your team just by practicing alone.