The poke check is not a very common move any more but if used properly can be very effective. You don't want to over use the poke check because then players will notice that and be expecting it. The whole idea of the poke check, it's unexpected.
When doing the poke check you need to be in your ready stance. When the player is within range, slide your hand to the top of your stick and poke it out quickly towards the puck. Keep your eye on the puck. Make sure that the poke check is done when the shooter is in tight and do it as quick as possible. Don't worry about the shooter getting tripped by you stick during the poke check; it will not be a penalty.