Hello all,
I agree with most of what Natalie has said, but here's some more...
To improve your running stamina and speeds, try some Fartlek or Interval type training - look it up on Google. This is by far the quickest way to see improvements in all areas of fitness.
Try to stay off the treadmills and get outside and run. If you limit yourself to treadmills, you only have the sensation of running over one surface. When you get to start your RAF training, you will be running outside, in woods, over fields, down roads, up hills, down hills etc... - all of these surfaces have different impacts on your body and to experience them all for the 1st time at IOT or Halton may be a nasty shock to your feet and legs and may cause you an injury which will set your training and career back a considerable time.
Try to focus your fitness training on how you want it to help you throughout your CAREER, not just as a means of passing a fitness test at OASC. Many people fall into this trap. It's all very well doing enough to get through a bleep test and a few press-ups and sit-ups. What about running in boots, in fighting order, over the hills of Otterburn? You can never be too fit, and doing it this way will only make the fitness tests easier and the least of your worries.
The bleep test, i find, is as much about how fast you can turn as how far you can run. If your technique is wrong, you could be Linford Christie and still fail, so it is worth having a practice at it before you do it, but remember, doing the bleeptest won't improve your fitness so don't do it 1 or 2 times a week as someone suggested. Do it twice a month, if that.
Good Luck