Tuning up and re-aligning your brakes is pretty easy. This will reduce wear on your brake pads, reduce squealing, and make the lever easier to pull. There are two main steps, realigning the brake pads and adjusting the tension in the brake cable.
To make this a little bit easier, there's a picture with all the terms you need to know about brakes to take full advantage of this tutorial.
You will need:
-You will probably need 5mm, but sometimes you will need 4mm or even 3mm
-Phillips head screwdriver
Note: If you have a multi-tool meant for bikes you will most likely have the needed hex wrenches and the screwdriver.
Step 1: Adjusting Your Brakes
First you need to figure out if you brakes need to be readjusted.
Your brake pads are out of alignment if
1. When the lever is pulled, the bottom of the brake pad is below the rim (sometimes you can see this from the other side of the fim)
2. If the brake pad ever rubs against the tire
3. If the brakes are skewed so that they touch in the back
4. Generally if the brakes look "off" or skewed
If your brakes rub without pulling the lever then they may need to be adjusted (especially if they look skewed) or you may just need to adjust the tension (see step #4).
If your brakes squeal you also want to do a slight readjustment but do not need to fully readjust. In this case see step #3.