What Goal Should I Set For Running The 800m Next Year?

How much did you improve last year?
How much have you improved each year?
As you get faster it is harder to keep improving by the same percentage or times.
A goal would be to go under 2:00 early in the season.
Then you should be able to get faster as you sharpen your condition, and get race fit.
You will have some days when you do not feel as well as other days so your times may fluctuate a little, but you should try to run each race as fast or a little faster than the last race.

10-12 is way too much. That takes you to 1:50, which only a couple of guys in all the high schools of the US are capable of.
It does depend on how much you improved last year, what your build is, if you are done growing, etc.
However, I would say that breaking 2 minutes early and focusing on 1:58 is a decent improvement. Check for any school records, meet records, state qualifying standards that would be in that nieghborhood.

Set a goal of under 2:00.
In the summer track season after my freshman year, I dropeed from 2:12 to 2:03. I think my sophomore track season I got a 1:59, and my juinor year I got down to 1:57, and 1:55 my senior year.
You may drop a lot at once, depending on changes in training, physical maturity and age, or you may progress very slowly, but just keep training hard, stay focused, and have fun, and you’ll drop some seconds.

I think you can do a 1:55 and possibly even a 1:50. Don’t try to peak too early though; Peak near state.

sub 2
you can do it!!

Depending on how hard you want to train I believe that shaving 10 to 12 seconds off. Make sure to mix in some strength training and avoid falling into the same routine.