The goal is to line up the target in your window in the bottom of your cockpit. Even with a good approach sometimes you will find yourself off a little. Small changes can be made in your dive but if you cannot get a good sight view of your target in the window, don’t dive. In real life your really wouldn’t want to turn around and attack your target again but if your goal is to put iron on target you are better keeping your altitude and coming around for another approach. In the picture above you will see what the target should look like in your dive bombing window.
Most of the time I set myself up to dive from around 3-5,000 meters or 10-15 thousand feet. Some folks start their dives lower but it really gives you less time to alter your approach if the target moves or if you are off a little bit. In addition, this altitude tends to protect you from most small caliber AA fire. Remember not to skimp on the altitude. A lower altitude does help with target acquisition but the higher you are the easier it is to get set up and dive.
A lot has to do with your target. A ship, airfield or bridge target is a lot easier to see than a tank. This is part of the reason that dive bombing fell out of favor with a lot of air forces as WWII continued. Slow, high dive bombing required a degree of precision that a lot of air forces didn’t have time to teach. Hitting something as small as an individual truck or tank is extremely difficulty. It’s beyond most real pilots and very difficult for virtual pilots as well. It is very difficult for me, and I’ve been dive bombing since 1942 Pacific Air War.