Before you venture off to one of these mythical 'high places' it's good to practice aid climbing at a crag you know well, perhaps as a wet weather option, so that you can slowly building the base skills you will require on real aid climbs - where mistakes may not be so forgiving.
You'll soon find that you'll need some aiders (tape ladders used to progress from one piece to another), and these can be tied from slings. You'll also discover that aid climbing is made easier if a single rope is used (10mm to 11mm), as this makes rope management and communication simpler.
In order to avoid being lynched by fellow climbers, take care not to damage the rock. Use only passive protection (no pegs!)
Cleaning the pitch
Artificial climbing also requires the second climber to take out the gear, or 'clean' the pitch, on jumars (see also Ascending). Once the leader has climbed the pitch and secured the rope, the belayer can practice cleaning. Again, this is where a single rope proves useful; it is easier, safer and less confusing to ascend one thick, single rope passing through all the protection, rather than two skinny ropes. Be warned though, cleaning the pitch can often be as difficult as leading.
On longer aid climbs it is much easier for the leader to pull up a haulbag containing provisions (food and water) rather then the second having to ascend the rope with it on their back. So it's worth practising hauling up an old rucksack on a second rope (haul line) that the leader trails up the route clipped to the rear of their harness.
As you master your skills you will begin to build up the specialised equipment necessary to attempt real aid climbs. This may include climbing exotica such as pegs, skyhooks, copper heads and a double set of camming devices. On top of this you may want to buy a pair of sewn aiders (these are usually far easier to use than a home made pair), plus a set of daisy chains, crucial if you are to practice modern aiding techniques. Mechanical ascenders, a small metal pulley, and perhaps a haul bag are just three other items on a long list that are useful on your first climbs.
Aiding in action
So you're standing at the bottom of your first real aid route. You've larks footed both daisy chains to your belay loop, and at the end of each, clipped in via a locking karabiner, is a single aider. Into this you've clipped a snap gate karabiner, or better still an oval karabiner - this karabiner will be used to clip into each piece of protection. In order to rest on your daisy chains, you may want to tie a short (20cm) sling into your belay loop as well. Onto this sling you can either clip a karabiner or (better) a fifi hook (a small, open hook that can be clipped and unclipped from slings or karabiners).
No one should even consider aid climbing without a helmet. Not only is it vitally important for impact protection in case of a fall, but also it is crucial to prevent pieces of rock smashing your skull while you are testing dicey placements. Now, having tied into your rope, you can begin climbing.
Place your first piece of protection as high as possible and clip your aider or daisy into it. Clip your fifi or karabiner into the daisy to get some tension on the piece. Apply weight to the piece via your daisy, or bounce up and down on your aider, until you're confident that it's sound. Now that you're confident that the piece is secure, step up the aider until you can clip your fifi/krab into the protection, rest and eyeball the next piece.
If you find that you need to spread your weight over both feet, or need to step up so that your waist is above your protection piece and you want to be in balance, you may want to clip one aider into the other via their snap gate karabiners. Standing in both aiders is far more relaxing, and once the next placement is made, you can unclip one aider and clip it back into the new higher piece for testing.
If you find yourself using vast amounts of energy you must be doing something wrong
Repeat this action is until the top is reached.
A few words of advice
If you find yourself using vast amounts of energy you must be doing something wrong. Make sure that you hang off your daisy chains and not your arms. After a few pitches you should build up a rhythm that suits you. The rope should only be clipped into pieces once they are at waist height. Clipping pieces above you only maximises your fall if the piece rips out and you fall.
Don't use pegs on practice routes!
Once the leader has reached the belay and tied off the lead rope he/she shouts 'rope fixed'. This is the signal that the second can now jumar the rope safely. If you are hauling, then use a second signal 'ready to haul', meaning the leader has threaded the haul line through a pulley and is now ready for the second to unclip the haulbag from the belay.
The second now steps up to the base of the climb, attaches their jumars, takes in the slack then begins ascending the rope. Each time they reach a piece of protection they need to remove it and rack it in some kind of order. Every ten metres, or when appropriate, the second should tie into the rope with a figure of eight. This is a back up in case of ascender failure. If the pitch meanders around, the jumaring may become quite complex and necessitate unclipping the top ascender in order to pass protection. While hanging from single ascender a kilometre off the ground you will understand the importance of tying back-up knots!