Is there a practice area with a long straight you can practice on, and do you have a rev counter on the screen?
If so, as a general rule while you're learning the ropes, shift up when it gets about three quarters of the way to the red zone (maybe 5000 revs or 7000 revs - depends entirely on the vehicle and it's engine).
That figure is completely variable, depending on the vehicle. You can increase it significantly if you're in a high performance vehicle. If there's a way of testing your time to get from 0-60 or 0-100, or perhaps over a set distance (quarter mile perhaps) run it a few times with the gear shift at 5000 rpm then a few times at 7000 - see which one gives you the fastest time. Tweak it from there.
After a while you'll know when to shift up by sound - which is imperative, as you can't really be watching the rev counter in a real race. You're only watching it now while you get to grips with things.
It also seems pretty obvious but it's worth saying - you'll only ever shift up when you're accelerating. Take your foot off the gas while you make the gear change (leaving the gas on while you're in between gears just revs the shit out of your engine, overheats it, and uses fuel without any power going from the engine to the wheels).
Once you have shifted up and put the gas back on you'll effectively be going at the same speed you were before the gear shift, but at lower revs - meaning your new acceleration will be better than it was when you were in the lower gear (torque has increased).
Similarly, you need to downshift when you're decelerating. (You'll never shift down when accelerating hard - save that shit for Chase HQ and Outrun).
If you're decelerating and your revs drop below around 3000 shift down.
The reason for changing down a gear (or two) is really just forward planning. You know you'll need to accelerate in a second or two, once you get past the corner you're on, and whilst you can accelerate from a slow speed when your engine is in a high gear and at low revs, it'll be a tortuously slow affair. If you want to accelerate out of this corner you want to ensure your vehicle is in a lower gear and revving around 3000 (that figure again is variable).
Again, you'll eventually do this by the sound of the engine, but while you're learning the ropes use your rev counter religiously.
As I say, get some practice in on a long straight stretch of a training course. Tell yourself you'll spend a couple of days learning to drive and avoid races.When you go back to racing in a couple of days' time you'll be in a much stronger position.
Do you know about apex cornering (going wide before a corner, cutting in at the right moment, going wide after the corner)? It's an essential skill for maximising speed over a distance, and something else you'll want to practice before racing, but for now just focus on working out the best time to change up gears, and then on working out the best time to shift down.
