Yep, all very good track suggestions. Here's a couple more for ya. Very easy tracks, and great for honing your cornering skills:
World Grand Prix 1-3
Flat's Formula Race
Zoon Spring
To reiterate what's been said already, give it time, bud - you'll get the hang of it. MTM racing can be somewhat frustrating early on (which is why many chose to be strictly rumblers lol), but you'll get there.
The best tip in the world I can give ya is just to keep racin. Specifically however, run a few tracks Phineus and I recommended and make a note of your lap times. As you continue to practice, make a special effort to take the corners smoothly while maintaining your momentum and minmizing side-to-side movement (no herky-jerky stuff). As your cornering becomes smoother and more efficient, you'll start to see your lap times fall, sometimes dramatically. After you've improved and you're fairly proficient at cornering you'll have to learn about racing lines--essentially the way you race a track, the paths you take in particular areas. Improving your racing lines will result in even lower lap times.
It's a process, like anything else, and it takes time. Hopefully you enjoy it enough to stick with it. It feels pretty good once you learn a few tricks of the trade and can keep up with other pro racers, giving them a run for their money, eventually earning a spot in the winner's circle.
If you need any additional help, log on and come into the Nitro Racing room. Heck I'd be happy to run a few with ya.
P.S. By the way, do you use a controller of any kind (joystick, wheel, gamepad)?