For the best free kick read this; If they are anything up to 20m out you should use the cross button to chip it over the wall(try to aim the ball between to defenders heads), just make sure you still bend it away from the keeper.
If the free kick is anything over 20m. you should power the power bar just a bit more then you think you should, while powering the kick pull back (down) on the controler this is so it will dip. As soon as you kick the ball push the controler left or right depending on which way you want it to bend (aim for top corners)..
Hopefuly you can score some great free kicks now Good luck