Here are the basic coaching points for instep drive shooting (notice that they go from the nose to the toe).

1. Keep your head down and your eyes on the ball.  Notice that this means you must have picked out the target before you actually shoot.  The eyes in no way affect the flight of the ball so it's best that they are focused on the ball itself to ensure a good, solid kick.
2. Plant the non-kicking foot along side the ball.  If you place the foot behind the ball your foot will be coming up as you strike the ball cause the ball to rise.  Of course this is sometimes desirable but for our purposes, we're referencing the basic instep kick.
3. Contact the ball on a spot near the center of the ball or slightly above the center of the ball.  As mentioned in step two, if you strike the ball on a spot below the center of the ball the ball will rise.  Striking the ball at center or slightly above will ensure the ball travels low and/or has forward spin (which is harder for the keeper to control).  Listen to the sound of the ball - a good, solid kick is easily recognizable by the sound it makes.
4. The knee of the kicking foot should be over the ball.  This will ensure the body is in the correct position. The most common mistake is for the knee to be too far behind the ball which will cause the kicker to arch their back away from the ball and hence produce too little power.
5. The instep is "locked".  The toe should be down and the ankle flexed upward in the direction of the calf.  "Locking the ankle" is very important but difficult to teach - it is not a natural kicking motion. A wobbly ankle will produce an inaccurate shot.
6. Approach the ball slightly from the side - not dead on.  This is probably the most common mistake young players make.  Approaching the ball from dead on leads to "toe poking" the ball.  By leading in from the side you will naturally tend to kick with the instep.
7. Follow through and follow the shot.  Kick through the ball - this will produce a more powerful shot.