I'm joining the army too, so lemme give you a little advice.
1. Go on runs every morning
It dosen't matter how far you can run now, it only matters how far you can run for your fitness test, which you'll do pretty soon if you're joining the army. In the U.K. you need to run one and a half miles in under 12:45 minutes which is the standard for Infantrymen. It falls under different levels, and depending on that level is how fast you need to do it. For example, a level 1 has to do it in 9 minutes, while level 6 gets 14 minutes. It really depends on what position you're planning to take, and I would read up about it online.
2. Download
This App
This app is great, I use it pretty much every day. If you're unfit as all hell, don't worry. It allows you to start off at different levels and so you can choose which one you want to start off with. I recommend starting with the middle level since the first one is really easy (Yes I went through that)
This will help improve areas aside from your running, though there is an option on the app to do that aswell. It shows you how to do each exercise if you don't know how to do that exercise. Make sure you watch that, because different levels have different versions of the exercise.
3. Eat healthy
Doing all this exercise is great, but if you're eating like shit you'll run like shit. You don't need to go on some crazy diet, just make sure you aren't eating McDonalds every day. If you're struggling with eating healthy (Which you shouldn't be) i'd recommend going on a diet, but only if that becomes a major issue. Normally you'll be fine if you just don't eat shit.
4. Play some sports
When I went down to the recruitment office a couple months ago, they were informing me about the training i'll receive as an officer. It falls into three terms, and each term you pick 2 sports. They will judge you off of the sports you pick, for instance, if you pick Shooting and Polo, then you aren't going to be as favoured as someone who picked Rugby and Running. Even if you don't have to pick a sport for your training, just do it anyway. If you're on base, chances are you'll play some form of sport, and being good definitely helps to make friends.
5. Just keep trying
If you keep trying, no matter if you feel like you are going no where, you WILL eventually get there. Sometimes you can't feel yourself improving, or even see yourself improving off of numbers, however, perseverance is an EXTREMELY important quality in the army to have. Some nights you'll be getting 4 hours sleep, and on those nights it's really about who really tries, and goes the extra mile to make sure their squad is safe. If you fall asleep on watch, you'll be reprimanded. Be the guy that, against all odds, keeps trying, and you'll find lots of success in the army.
Any further questions, just ask me. Also, as a disclaimer, my physical standards are going to be below yours since i'm female. Don't take all the numbers I say as literal, as each army has different requirements. Check to see what yours are.
[doublepost=1471273787][/doublepost]Use that app as your routine, it's really fucking good.