Believe it or not most aiming trainers are a waste of time. You don't aim a pool cue like you do a rifle, it's more like golf in that most of the 'aiming' that a good player does happens before they ever get down on the shot. Therefore, if you are having trouble with aiming, I recommend focusing on what you do before you even get down on the shot. Face your target squarely and set yourself in a good solid stance and then let your eyes and your instincts do the rest. Assuming your fundamentals are correct, you will deliver the cue ball to where your eyes are looking, I promise.
Having said that, if you're still having trouble seeing where you need to hit the object balls, a good thing to try is to step back from the table like six feet or so and look down the line of the object ball from there. It's actually a lot easier to see the lines from farther back. That is why the game always looks just that little bit easier when we're sitting on the rail watching than it does from behind the cue. Try it.