I would add only a couple of things to 2 Cdo's post:
Whilst maintaining yourself at a superior fitness level, try being a superior soldier. In YOUR case, you'll be a Private. Do what you're told cheerfully, to the best of your abilities ALWAYS, volunteer for lousy jobs CHEERFULLY. Forget the word "WHY", and the phrase "HOW COME" (unless seeking clarification regarding a procedure). Learn your trade THOROUGHLY, be proficient at ALL aspects of it, not just those that turn your crank.
I don't know how it works in the Reserve world, but a pretty safe bet is that any available vacancies are loaded by your unit on a merit basis - this means being a superbly fit thudf**k won't cut it.
Good luck - never lose sight of the end objective, but on a daily basis, deal with the smaller tactical bounds placed in front of you - one at a time, BMQ, SQ, etc, etc.
Edit: Typos