The drop in is the most relaxing way to enter transitions/ ramps. Before learning any transition tricks, you should be able to do a drop in, i.e. riding down the ramp. Before you learn the drop in, however, you should have developed a secure feeling on your board, especially for pushing and turning. Find a ramp with a large radius, i.e. a ramp which isn't too steep, to learn the drop in.
DROP IN - STANCE: REGULAR
Place the tail of your board on the coping (the round metal pipe on top). Step on the tail with your back foot and shift your whole body weight on it to have complete control. Carefully place your front foot over the bolts of the font truck, but keep your weight on the back foot. In the beginning, try to keep this position for a while and then take your front foot back off the board. Once you have developed a feeling for the position, it is time for the next step towards the drop in.
The most important thing during the actual drop in is shifting your weight properly. Right now, you still have the main portion of your body weight on your back foot while the front foot is placed over the bolts of the front truck. Shift your weight forward by leaning your body toward the front foot. While you're doing that, crouch down a little. With more weight on the front foot, the board enters the transition.
All four wheels are in contact with the transition now and you begin to roll. Keep your center above the middle of the board in order to prevent falling forwards or backwards. If you're doing it right, you'll ride down the transition without problems and successfully pull off the drop in.
In the beginning, it is better to lean too far forward than to lean too far back. You can also practice the drop in on a bank first, rather than on a quarter pipe.