What position do you play? What are you goals? Providing us a better idea about what you'd like to accomplish with your conditioning will help us provide some ideas for you.

Best,

Steven Ellis
Former Chicago Cubs pitching pro
http://www.thecompletepitcher.com

Children under 16 shouldn't lift weights because of a risk to growth plate part of growing bones.

Sorry Sidd but I disagree and so does the medical profession (the American Academy of Pediatrics)...

Generally, if you're ready to participate in organized sports or activities such as baseball, soccer, or gymnastics, it is usually safe to start strength training.

A child's strength-training program shouldn't just be a scaled-down version of an adult's weight training regimen. A trainer who has experience in working with kids should design a program for you and show the proper techniques, safety precautions, and how to properly use the equipment.

Kids as young as 7 or 8 years old can usually do strength-training activities (such as push-ups and sit-ups) as long as they show some interest, can perform the exercises safely, and follow instructions. These exercises can help kids build a sense of balance, control, and awareness of their bodies.

Specific exercises should be learned without resistance. When proper techniques are mastered, small amounts of resistance (body weight, band, or weight) can be added. In general as kids get older and stronger, they can gradually increase the amount of resistance they use. A trained professional can help your child determine what the appropriate weight may be.

As with any sport, it's wise to to visit a doctor before beginning a strength-training regimen. If the doctor signs off on the idea, you'll need to make sure that you be properly supervised, using safe equipment, and following an age-appropriate routine and remember, resistance should be light if at all.

I play baseball and run cross country im really fast but i need some wind to be better in cross country

You need repetion. That is the key. Not the amount of the weight. You just have to do repeated exercises that will work the muscles needed. Acurate strength training comes from repetetive training.

I play college ball and my workout routine consists of a lot of core work. I use the medicine ball and different core workouts to work on my power and explosiveness. Some plyometrics also help with explosiveness and agility. I also do a lot for my arms and legs. Like tricep dips, curls, inclined dumbell press, rows, and forearm stuff for your arms. Squats and step ups while holding dumbells are good for your legs. Baseball doesn't require too much heavy lifting though because you aren't trying to bulk up like you would in say football, but rather get stronger and more explosive while maintaining your athleticism and flexibility. I always finish lifting by stretching and either swinging my bat or throwing. Also a good way to develop bat speed is to get a lead bat, that is a wooden bat that you fill with lead or some other type of weighted material that makes the bat heavier. Swinging it after every workout will help make your normal bat feel lighter when you step up to the plate.