One important aspect of a soccer game, which does not get practiced enough, is the penalty kick. Often, a late penalty kick or a final finishing in a penalty kick shootout determines games. For example, with Italy and England in the 2012 European Soccer Championship.
Here are some guidelines to help you place your best penalty kick. The first order of business is to keep it simple. The best penalty kick takers I have known kept their penalty kicks simple. There was no flashy outside the foot upper corner shot that hits the crossbar and went in. They kept the same approach each time and always had placement over power in their kick.

Here are some guidelines:
1) Take the same approach every time. Usually four to five steps back and few steps to the side. Approach the ball with a moderate pace. Not to fast, not to slow. Keep your hips neutral and square to the ball in order to keep the goalie guessing. Goalies are taught to look at the players hips to help them read the shot.
2) Always place the ball the way you want it, this is where you start your system Having the same setup will give your confidence in your kick. Some players like to hit the logo of the ball, whatever it is it should be the same every time.
3) Make sure you check the footing of your plant foot. Especially in grass fields. By having a solid area to plant will ensure you a solid kick.
4) Kick the ball more the top/middle of the ball with your instep. In order to hit with your instep you need to open your foot and lock your ankle. You should place the ball in either corner of the goal. Preferably in the side netting of the goal, with enough pace to get it past the keeper.
5) Keep the ball low. A low hard shot is much harder to save then a high shot for a goalie.
6) Stay over the ball, don’t lean back as this will cause you to kick the ball over the goal.
7) Prior to your approach, take a deep breath and relax. Start to envision the ball going into the goal. This is also where you decide which side you want to kick the ball. Pick a side and go for it!
8) Don’t get psyced out by the goalie he is just trying to distract you. Just stay focused on your target. Pretend he is not even there.
Helpful Tips:
1) Practice penalty without a goalie first to ensure your work on your technique first and then add in a goalie when you feel comfortable
2) Practice kicks whenever your can, add pressure if you miss a kick you have to perform 4 sprints, etc.
3) Have fun, if you get worried about missing then you will.