Shooting Technique
As far as technique, emphasize proper balance while shooting. Encourage your players to lock their shooting ankle and to use their touch to set up the proper approach on the ball (this should be close to a 45 degrees, not straight on). For a video on proper technique, you can check out http://www.insidesoccer.com/is-web/movie?id=304 (when David Alred says "get your kicking foot down," he is talking about landing on your shooting foot--this is critical to getting power behind the shot and a big difference from striking a long ball or pass). Also, you often hear coaches tell players to get their head over the ball when shooting to keep the shot from flying over the crossbar. The flight of the ball actually has nothing to do with your head, but more the relationship between your shooting knee and foot. If a player is shooting the ball high every time, make sure their knee is not too far behind their foot when they make contact and tell them to focus on striking the middle or top half of the ball.
Shooting With Combination Plays
With shooting exercises, I prefer to get my players as many repetitions as possible, allowing proper technique to become second nature for the kids.
http://www.insidesoccer.com/is-web/movie?id=244 -- This exercise brings three shooting scenarios into play and offers continuous shooting on goal. It is demonstrated with younger players, but I do it with my U19 team and they get a lot out of it (I obviously ask them to raise the bar a little higher as far as technique and production than I would U12s). Also, you only need one goal, which is often the scenario on the Arsenal practice fields. Have the players rotate between the three lines, and change in different goalies if you have them. Make sure the cones are the appropriate distance away from goal for your players (I also like setting up a cone as a stationary defender for the first line of players to perform their move around). And emphasize quick shots--we want the players to become comfortable in quickly creating a window to shoot on goal, rather than taking a ton of touches and potentially losing their scoring opportunity. The objective is to score, but if the players have the choice you would prefer them to shoot low and to the far corner, as this produces the best rebounds for teammates if the goalie can not field the shot cleanly.