When training for track and field you will want to perform movements that will work your fast twitch muscle fibers since this is what you are mostly going to utilize in these activities.
Any movement that is done over a short period of time and requires a large contraction rate is done with these fast twitch muscle fibers. Since this describes most track and field activities it will be what you want to concentrate on.
In order to accomplish this, when you are in the weight room doing your strength training exercises, perform sets of 5-8 reps so you can focus on lifting a heavier weight over a shorter duration. If you wanted to you could even adjust this down further into the 1-3 rep range so that you are strictly focusing on strength and power. Try and generate as fast of a movement as you can through the concentric phase (contraction portion) since this is the prime way to generate power.
When performing in the lowest rep range you should try and shoot for a higher number of sets such as 3-5 to get the optimum volume for improvement. If you are working in the 5-8 rep range than aim for 2-4 sets instead.
Also focus on doing more explosive, compound lower and upper body exercises, particularly squats and chest presses. This will work the necessary muscles you need for most of the activities involved with this sport.
Finally remember to balance your weight training sessions with your practice sessions so you do not over work your CNS. You need to keep in mind that the CNS takes longer to recover than your muscles do so even though you may physically feel alright to train you may still not be fully recovered. It's a good idea after any really heavy sport specific practices or after a hard leg workout to take one day off for complete rest. This should drastically reduce the chance of CNS overtraining.
Having a well-balanced approach to your training, both on the field and in the gym, is the best way to show improvement and enjoy the process of training itself.