Fitting v-brake pads

Step 1
First, squeeze the brake arms together to get the cable 'noodle' (the curved metal pipe) out. Now you can remove the old pads. Undo the bolt with a 5mm hex key, and make sure to keep the old nuts and washers. New pads may or may not come with them, but they're very easy to lose so some spares might come in useful one day.
Step 2
Now you can fit the new pads. If you look at the nuts and washers you'll see there are thick and thin spacers. These are used to get the spacing right between the pad and the brake arm. The idea is for the arm to be upright when the brake is applied, so experiment with the spacers to get this right.
Step 3
Placement of the pad on the rim is crucial. Too high and it'll hit the tyre, too low and it will go into the spokes. With the brake arm in the 'on' position, and the bolt loosely done up, get the pad in place then tighten it. You'll find that the pad will rotate as you tighten the bolt, so apply as much pressure on the back of it as you can, and start tightening the bolt with the pad slightly anti-clockwise to where you want it to be, so it ends up in the right position.
Step 4
Now your pads are in place, get your cable right. Wind out the barrel adjusters on the brake levers a bit to give yourself some room for adjustment, then undo the cable clamp on the arm itself, squeeze both arms together and pull the cable through to take up the slack. Do the clamp up tight, and turn the brake barrel adjusters in to release the tension, keeping the pads as close to the rims as they'll go without rubbing.
Step 5
At this point, you can either stop, or keep winding in- depending on what sort of feel you want from the the levers. If you can pull them back to the grips, they're too loose.
Now check the spring balance on the cantis (brake arms). This will be either a 3mm hex bolt or cross-head, and they're used to alter the amount of force needed to get the pads to the rim, and fine tune the distance between them- giving balanced, smooth braking. The lighter the spring pressure, the lighter the brake 'feel' at the lever, so when both pads are an equal distance from the rim, wind out the adjusters equal amounts to achieve the lightest spring tension you can get away with- or simply adjust to taste.