So last year you were focusing on speed and ran 58/2:09, this year you are focusing on the 800 yet you are going to drop 5 seconds in the 400 and only 6 in the 800. Does that sound reasonable to you? Cross country training isn't ideal for the 400. While running is better than not running, running slow (1:26.4 400m pace to run an 18:00 5k) does not help you run fast (53 400m pace to run a 53 400m). You may run personal best times in the 400, 800 and 1600, you are still developing physically, more experienced and training harder, but you won't run what you are capable of focusing on three events. Focus on the 400-800 or 800-1600, my suggestion being the 400-800. Develop your speed now, move up to 800-1600 your junior and senior years. If you do run 53 you might consider sticking with the 400-800 through your junior year. Rather than weights i would do plyometrics. It better mimics running motion and avoids the imbalances you can get lifting weights (which leads to injuries).
I would try plyometrics if you can leg press two and a half times your body weight. You'll want to gradually introduce plyometrics into your training, no more often than twice a week, and take a two-week break from all plyometric work every eight weeks.
To warm up for a plyometrics workout, jog for at least five minutes, and follow that with five minutes of light skipping, gentle jumping jacks, and high knee prancing. It’s best to perform the jumping drills on grass so you have some cushioning. A football field is ideal so you can use the yard lines, but any stable, cushioned surface like a track will provide the "give" you need. After the drills, do an easy run or reduced-volume speed session to round out your workout.
Launch into each drill with your feet shoulder-width apart and knees slightly bent. Perform two to four sets of each drill.
Balance Drills
The Payoff: Improves balance; strengthens ankle, knee, and hip joints.
1. Jump and Sticks
Jump from and land on the balls of both feet. Jump high, not far. Land with knees bent and hold two to three seconds before jumping again. Alternate jumping 10 yards forward and sideways.
2. Two-Way Hops
Start balanced on your right leg. Hop two to three feet forward onto your left leg. Hold for two seconds to regain balance. Stay facing forward and hop back to the start position onto your right leg. Now hop onto your left again, but move sideways, then back. That's one set. Do three more, then repeat the drill starting on your left leg.
Elasticity Drills
The Payoff: Strengthens all lower-body muscles; improves the spring-like ability of the muscles and tendons around the joints.
3. Skip Ups
This is an exaggerated skipping motion. Drive your leading knee high, until the thigh is parallel to the ground, while popping off the ground, with your toes pointed.
4. Standing Long Jumps
Swing your arms back, then forward as you leap, and jump as far as possible, landing on both feet.
Power Drills
The Payoff: Improves stride power, or the force of each push-off.
5. Jump and Sprint
Do a standing long jump (see Drill 4), but at the moment you land, sprint for about 10 yards.
6. Triple Jumps
Start with a standing long jump (see Drill 4), but land on your right foot, quickly hop forward onto your left, then hop and land on both feet. Aim for maximal distance the whole way.
Ideally, the number of jumps should not exceed 80-100 /session for beginners and athletes in early workouts, 100-120/session for intermediate athletes, and 120-140/session for advanced athletes who have completed at least 4 weeks of plyometric training.