There are 4 basics kicks that every karate student should know - the front kick, side kick, roundhouse kick and back kick. The first three start from the same chambered position with the knee raised in front of the body. Remember that for these three kicks, the knee is the sight for your weapon: where your knee points, your foot lands. Most of the kicks in Kenpo are below or at the waist height.
Each of the first three kicks has two forms: a snapping form, and a thrusting form. In most cases, the self defenses in Kenpo use a snapping form, but it is important to know and practice both. As you learn, practice the kicks that give you the most difficulty first. It is easy to fall into the bad habit of only learning what presents the least difficulty. To be well rounded, you have to work on the hard stuff all the time.
The Front Kick
Each kick starts from a proper, balanced stance. The kick has four steps: the chamber of the leg, the extension of the leg, the return of the leg to the chambered position, and the return to the stance. The front kick uses either the ball of the foot, or the top of the instep as the striking zone. If you are using the ball of the foot, remember to pull the toes back before impact and if you are using the top of the foot, point the foot as far forward as possible, straightening the toes. And remember to pull it back as quickly as possible after making contact. A snapping kick is momentary contact while a thrusting kick is all about going through the target. If you wish to have more control, then you have to build up the muscles by kicking slowly and holding the kick out at the end of the extension. As you gain control, you can add weight to the end of the foot, but never kick quickly using weights as you may damage your knee ligaments (amongst other parts).
In the photo sequence below, Sensei Derek Griffioen demonstrates a snapping front kick from the back leg and a left neutral bow. A snapping kick may also be delivered from the front leg by first retracting the leading leg into a 45 or 90 degree cat stance, then extending the leg from the chambered position. The rest remains the same.
The thrusting front kick develops more power by leaning back with the torso and pushing the leg forward using the hips. There is a sacrifice in speed and the thrusting kick is completed by landing into the target, not retracting the leg.
A really good drill for control is to do the four kicks in sequence. Start with a front kick, follow it with a back kick, then a side kick, and finally a roundhouse kick without dropping your foot to the floor until you have completed the roundhouse kick. Repeat on the other side.
The Side Kick
The side kick uses either the outside edge of the foot (snapping version), or the heel (thrusting version) as the striking surfaces. In either case, you need to pull the toes back toward the knee as you extend the leg. For the snapping version, from either leg, the foot that remains on the floor must, at a minimum and depending on your flexibility, rotate so that the toes point to an outer corner. If you are less flexible, you might want to consider more rotation in the grounded foot if necessary. For the thrusting version, it will be necessary to point the toes of the foot on the ground in the opposite direction to the kick for stability. The kicking leg in the thrusting version is pulled across the waist (a different chambering position), and then thrust at the opponent in line with opposing foot.
The Roundhouse Kick
The roundhouse kick uses the bottom of the shin as its striking surface for both the snapping and takedown (thrusting versions). In the snapping version, the foot is retracted to the chambered position before landing, while in the takedown version, the foot ends up on the opposite side of the target before landing: there is no retraction. Notice in the photo of the extended kick the position of the back foot and the amount of rotation required. Don't under rotate the back foot or you may damage your knee ligaments. The difficulty in this kick is rotating the foot for the kick, then rotating it back when the snapping kick is completed.
So what have you noticed so far? The chambering position is the same for the snapping front, side and roundhouse kicks. This makes it very difficult for your opponent to know which kick you are going to throw.
The Back Kick
The back kick always use the heel as its striking surface. You want to avoid raising your leg to the outside as you kick so as to protect your groin from a kick from behind. Notice that the foot is not straight up and down but the toes are slightly to the outside. And if you are trying to kick higher, then you have to crouch lower and bend forward to get the leg up as you extend your leg as there are anatomical limits to how far back the leg may extend from the hip.