Sprinting is good. What is it? Everyone complains bodyweight exercises are not great for mass/strength building since you can't up the weight. The analog for increasing weight is to start doing them explosively. Sprints are excellent all the way around and I treat them like any other lift with a set/rep scheme. Make sure your body mechanics support sprinting (you were a runner, so you should be ok). Lots of people want to sprint and get hurt trying.
First off, resting between sprints is a requirement. Resting meaning walking slowly or just sitting down. You must recover.
Second, distance for sprint is the same as for recovery. So if you sprint 100 m, then you walk back that far.
Warm up. This means doing the distance a few times gradually increasing speed. Again, just like weights. Best warmup is doing whatever lighter and slower. Don't risk injury.
Sets and reps work this way: A rep is a sprint. start with 3x3 and work your way up to 5x5. Normally the timing is sprint, 60 - 90 sec. recovery, sprint, recover, ...
Treat sprinting like any other lift. Look at sprinters. They don't look like other runners.
Last point -- if you are, say,doing heavy deads that day you wouldn't do heavy squats, would you? Same with sprints. This is good since you can get a kick-ass and short workout on off-lifting days that does deliver good results. Fortunately sprints are like no other exercise, so
Oh and various schemes for trying to up the load, don't use weight vests -- I found that going heavy enough to make a difference really screwed up sprinting mechanics so I was losing ground. Ditto other weights. Best simple metric for success is time spent sprinting over a fixed distance. If your path takes say 30 sec. to do initially, over time (weeks) you should do it faster. Then increase the distance to keep the time the same (yes, this is escalation density training). Increase rep and sets too. Chances are very good that you won't hit 5x5 so easily.
Course, everyone will tell you I'm usually full of shit... YMMV