Hi, Jill,
Welcome to this forum. I am not Cathe and perhaps she'll have something to add later. I'm a former track "star"
from the old days of 20 years ago. Provided things haven't changed too much in the world of running, I will give you a bit of advice. Start competing with yourself. Find out your time for the various races, like 100 m dash, 400 m dash, 800 m, etc. You can probably research times in your district and find out what kind of times will earn you a place at a track meet. Find out what races you would be able to be competitve in. Then work on strength, endurance and form. Weight training would also be excellent for you, 2 or 3 times per week.
As for stretching and warm ups, I usually run a light jog for one or two laps and then get some good stretching for the hamstrings, quads, calves, inner and outer thighs and glutes. Then some runs like high jogs or butt-kick runs, shuttle runs, or football runs to work on the explosive leg muscle fibers. Beyond that, practice your races and running lengths longer than your races.
Best of luck to you!!! Cathe will have to tell you about her nails.
Amy