A slide is a glide

Ripken Baseball

How do you go from running to sliding? 
Take a seat.  

 It's strongly recommended that players on your club work on this phase of the game to the point where they can leave their feet without risking injury. It is not expected that all will be complete sliders—that is, baserunners who can go either way and be proficient with both feet and hands—but you should expect all players to be able to get to the ground without endangering life or limb.

Since a slide is the quickest way to get to a base and hold onto it, or avoid the tag, its importance cannot be over emphasized. The words "leap" or "jump" should not be used when describing a slide. A slide is a glide.

To go from the run to the slide, merely sit down, throwing the hands back over the head. Tuck the take-off leg under and keep the other leg up off the ground, lowering it to touch the base as you approach the base. You should always run in a straight line—there is no need to approach one way or the other. If a straight-in slide has been executed properly, both buttocks and the back of the uniform shirt should have dirt on them. By throwing the hands back over the head, a runner can extend the leg, have a faster glide and eliminate any injury to the hands or wrist.

The following tips can help players with sliding problems: 

It is suggested players work on the grass in the outfield with spikes removed. Have players, either in stocking feet or sneakers, and keep the base loose. Sliding pants can be used for this work.

A player should first practice sliding on the side that seems natural to him or her. 

The following example describes the position when hitting the ground: 

TYPES OF SLIDES 

Straight-in slide

The straight-in slide is the slide used when trying to beat the play by arriving and holding the base in the fastest time possible.

 Actions are as follows:

When stealing, start in a direct line for the bag. 

Experience will govern the take off of a slide: Don't start the slide too short of the base 

At a point approximately eight feet from the base and at top speed, the left leg folds to the sitting position as you hit the ground, with your arms back over the head, and your right foot extended forward to the bag. The arms are thrown back to prevent injury to the knees, hands and wrist.

The pop-up slide

This slide is used by a runner to regain his feet quickly for possible advance beyond the base he is approaching. All the actions used for the straight-in slide are used here. As the right foot hits the bag, however, the body is thrown forward. A slight push with the hands then brings the runner to his or her to his feet.

The experienced slider executes this slide in a different manner. He takes off closer to the bag. The right leg (held high) goes over the bag, and the left leg (still folded back) hits the bag with force and throws the runner to his or her feet.

All pop-up and straight-in slides should be made on the left side as the runner comes to his or her feet facing the direction he or she will be going.

Sliding tips 

All slides are determined by the actions of the fielder. Approaching in a direct line, keep your eyes on the fielder to determine where the throw will be.

On the throw to the fielder's glove-hand side (usually the left), the runner drifts to his or her left and slides on the left, extending the right leg to catch the bag with the toe.

On a definite out, the experienced slider may purposely miss the bag with the right foot and attempt to come in with the hand.

With the ball coming to the infield side (right side), the slide is executed in the same manner with one exception: The base runner slides on his or her right-hand side. If the runner can only slide on one side, he or she can do nothing but grab for the bag with the hand.

Good slides are made at top speed; never slow down to slide. 

Wrists are injured when the runner jump-leads into a bag and attempts to ease the impact by using his or her hands, or tries to break the impact because of a strawberry or skinned knees.

As sliding progress continues and runners gain confidence, they hit on the foreleg and appear to ride the calf of the bottom leg, causing skinned knees. Some protection is gained by folding the inner and outer stocking in pleats below the knee and holding it in place with a stout rubber band or tape.