Speed is relative to the situation and numbers don't lie. However; a great base runner is both smart and fast. Natural instincts can make an average speed athlete look like they are fast. Experience helps but let's be honest, athletic ability is something a person is born with. You can hone your skills but some are faster than others regardless of their efforts.
One of the factors that many coaches overlook is "reaction time." Analyze each individual by breaking down the base-stealing scenario. Why do some girls you know are fast constantly continue to have close calls or thrown out? Many times it is due to reaction of the situation. They are given the steal sign. Did they leave immediately on the release? Did they leave with urgency? Did they slide? were they focused on their stride and pumping forward? Consider the scenario of a girl reacting to a passed ball. Did she react?
Most humans have a reaction time of .2 seconds. With practice you can hone that but what I have found are some tricks and gimmicks to help put a positive reaction time in the girls head. Most of these came from Sharon Drysdale and Bill Edwards, iconic coaches at the highest level.
Let's go with a straight steal first. If a girl knows she has the steal sign it is crucial she get a good jump. The best and most efficient way is to be in motion at the release. For this reason, I teach the method of the "rock and go" with the push off foot on the bag closest to the target base. Standing with the lead out foot back, behind, and off to the edge so when making the stride she doesn't snag her toe and trip. Basic runner's stance. She begins her forward motion so at time of release she is already in motion to leave at release. This motion does numerous things. Cuts down the reaction time to a minimum plus base umpires are less likely to catch or call an early leave due to the body already in motion. When sitting along a fence many fans scream she left early but take time to go out on the field and watch this transpire. It has a totally different look from a base umpire's perspective.
The other factor is the advancement on a passed ball. If a girl is incorporating the method described above to get a lead on the release, she needs a triggering mechanism in her head to know when to "go." What we practiced is if the ball hits the ground you go from any base but 3rd. Stealing home is a different monster. The rest of the bases we go regardless unless told exclusively not to. The time it takes a catcher to react to any pitch in the dirt is enough time for most all base runners to advance if they go wholeheartedly and slide when they get there. Even a pitch that goes downward into the dirt and stays in front of her forces a catcher to look downward and offsets the reaction time to favor a runner. In the dirt you "GO" and "GO" hard to the bag. You get caught it's on me not you. I'll take the blame. You get there safe and the cheers are all for you. This mental trigger when practiced gives an average runner the mental edge she needs to run with confidence.
Just make sure they understand that go means go not "I think I can make it." The only time I get upset is if they don't run with the urgency they should or go in standing up. I want my girls to know I want more than 1 base if we can get it. Go in fast and hard. Get up fast and ready to go again. Why take 1 if your reaction has caused another defensive mistake.
Rub it in when you can and rattle them!!!!