Wheel truing is actually something that is very easy to do. Even if you have no experience with mountain biking or truing a wheel, it doesn’t take a rocket scientist to accomplish it.
The first thing to do is make sure that none of your spokes are loose. To check, grab each spoke in turn and try to shake it back and forth. If the spoke wobbles, or makes pinging and grating noises, it’s loose. If it’s loose, add tension to the spoke by turning the spokey anti-clockwise with your finger and thumb pressure.
Keep turning and shaking until the noise is gone and the spoke doesn’t wobble or move. Move on to the next spoke until you’ve gone all the way around the wheel and checked them all.
Now, it’s time to see just how true the wheel actually is. Turn your bike upside down then spin the wheel to see where it comes closest to rubbing on the brake.
You may need to rotate the wheel backwards then forwards to locate the middle of the bulge on the wheel. Tighten the spokes which run on to the other side of the rim. If those spokes are already tight, you’ll need to loosen a few of the spokes which run to the bulge side of the hub.
Truing a wheel is easier than you may think, although it can be a little tough with some wheels. If you need to loosen spokes, be very careful that you don’t break them. They can be very tough to loosen on older mountain bikes.