This can be a difficult achievement for a casual gamer to achieve, though there are ways to make it a little easier on yourself.
Qualification laps set by CPU players will generally be a few seconds slower than their race times, so qualifying high is essential to avoid the crush at the first corner. Pole Position is not essential, but aim to be on the first couple of rows on the grid, which will help immensely when you've set your...
2. Gear Ratios
Adjusting your gear ratios for improved acceleration will put you ahead of the pack into the first corner, meaning that the race is yours to lose. Spartan92x on the x360a forums recommends the following ratios, and they worked well for me.
Set the race length to 1 lap. You should be leading by the first corner, so why make it harder on yourself!
4. Finishing Position.
Aim for a top three finish every time, though if there's a course you're struggling with settle for top six! Doing this might create problems in maintaining your position at the top of the table, so if another rider is in front of you in the table, increase your chances of finishing ahead of this rider by...
5. Restarting Races
At the start of the race, a few random riders will burnout at the start. This is in no particular order, so if you restart the race a few times eventually the rider you want to beat will get a bad start, meaning they'll be struggling for a top 8 finish.
One other thing is to master is getting a good start. On a dry track, hold the trigger in very slightly, to around the point where the pad rumbles slightly. Your rider will then move forwards slightly as soon as the lights go out. At this point apply maximum throttle.
On a wet track, hold the trigger in the same as on dry, but when the lights go out slowly increase pressure on the trigger until you're at full throttle.
Good luck, this is the first solution I've written so be kind!