Try aiming at the posts.
In high difficulty matches it is sometimes necessary to be more tricky in front of goals. This means that instead of running a striker in and trying to shoot, try...
(1) running him around in front of goals hoping for a free kick or a penalty. Trust me, in desperate times I have done this. All you do is keep changing directions and the AI will try to tackle. If you time it right and move away you will be fouled. Hopefully for you it is easier to score from free kicks and penalties.
(2) Do crosses. This is my main source of goals. Either lob cross it and try to latch a header on to it, these are very hard for the goalkeeper to save. Or cross it along the ground, get some space, and try shooting there.
(3) Instead of using one striker, use two. If you have enough room, instead of shooting, do a quick pass to a fellow striker to slot one home. I have done this several times. Walk the striker into the penalty area and lure the goalkeeper to you. At the last second pass to a teammate who might find an open goal.
(4) As I said before, aim at the posts. This might me a little risky as the ball has a better chance of bouncing back or missing completely. What I try to do as a I shoot is aim for what one would think is a miss. Instead, the computer will automatically try to curl shots that might miss (go ahead, try it - a good striker will automatically curl missing shots.) What I have noticed is that if you purposely try too miss (by pressing <- left or -> right instead of both for a diagonal shot) the ball riccochets in off the post a lot of the times.
I hope this has helped.
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