The long-hang kip is a bit different from a glide kip performed on the low bar. Though the two skills require similar upper-body strength, the timing is quite different, as is the swing. In general, this is a skill that takes a lot of practice and repetition before the gymnast figures out what the correct swing feels like and transfers that swing into her muscle memory. As with the free hip circle, I can offer a few tips and tricks, but practice is what is going to get the skill to click.
This skill begins with a jump to high bar. If your jump isn't solid, the long-hang kip will be more difficult. You do not want to jump in such a way that your back is severely arched when your hands hit the high bar. In order to have a smooth swing into your kip, you should reach the high bar with a tight, straight body. Depending on your height and the bar setting, you may benefit from reaching the bar in a slight, tight hollow rather than a straight, stretched body. Either of these options is great as long as there is no huge arch to interfere with the natural motion of the swing.
As you reach the high bar and begin your swing, you want to try to keep your feet behind you. A pretty common mistake is bringing your feet up too high on the upswing. When the upswing is too high, it's difficult to continue that momentum as you bring your ankles to the bar and begin to kip up. Swinging too high will work against you by bringing your momentum straight down, rather than back and up. You want to control your swing by keeping your feet behind you at the beginning of the swing.
However, this doesn't mean you should ignore the tap. You still need to perform a slight tap as you would with a normal tap swing. Keeping your feet behind you before the tap will just help to control your height and speed.
After the tap, you should swing up so that your body reaches a nice, stretched hollow. This is the point at which you want to raise your ankles to the bar and begin to kip. From this point forward, the kip is much like a regular glide kip. The same motions apply - the "pull up your pants" motion with the legs, a slight wrist shift, and ending in a front support. Of course, if you are connecting a cast out of your long-hang kip, you will need to finish with your feet in front of the bar and your shoulders leaning over as well.
These are just some basic tips. A lot of it, as I said, is just figuring out the timing that works for you. Happy kipping!