Learning to set gear when climbing will open up a whole new world. You will find yourself climbing in some of the most beautiful settings on the planet. The traffic that traditional routes see is significantly less than the traffic that you will see at the foot of a popular sport climbing wall. Learning to organize your gear so that you can reach it quickly, selecting the right piece the first time, knowing when it is placed correctly, and knowing when you have placed enough are all critical factors in setting gear while climbing. Once you have mastered this talent you will climb with greater confidence and with greater frequency. You will no longer be limited to routes and areas developed by others; you will be free to experience the adventure of traditional climbing. Knowing what you can and can not trust will only come with time. Don't let your pride keep you from walking away from a climb that you're not mentally or physically prepared for.
Ensuring that your gear and rack are organized will greatly increase your efficiency in climbing and setting gear. Knowing where a piece is will allow you to quickly find and place the protection. Time wasted looking for the right nut or cam, while standing on a questionable hold, will quickly drain what energy you have. Placing your gear in a logical pattern (bigger pieces to the back) will allow you to spend less time looking and more time climbing.
Although proper use of gear is better learned while standing with both feet planted firmly on the ground, gear selection can only be learned while on the sharp end of the rope. Knowing what piece to use and when to use it will only come with experience and time. You may feel confident leading 5.10 on a sport wall or on plastic, but starting out well below your ability will ensure that you have enough strength in reserve to make it past the steep learning curve of gear selection. With the use of CAMs the selection process has become much easier as you can often find several CAMs that will work for a single placement. It is my preference to set my passive protection first, leaving my CAMs in reserve for the unknown ground above.
Each piece of equipment on our climbing racks has an optimum placement; a setting in which the gear will easily hold a whipper. These bomber placements are not always easily found and you may find yourself settling for some not so perfect placements. Even if you just set a piece a few moves lower, you should set another if it appears that it will be bomber. Take the time to practice setting pieces while standing on the ground. Become familiar with how a good piece should look and feel when set properly.
Quantity vs. Quality
When learning to set gear, most tend to use a few more pieces than are necessary. There are several good books on the theory of when and how many anchors should be set. Spend some time researching this topic. You will find that if you have an understanding of the theory behind the quantity of pieces you should set on an average climb, you will be much more likely to trust a quality placement to hold a fall from a greater distance. Knowing that you have a few bomber placements allows you to climb with much more confidence than having several marginal placements. Be safe and remember to enjoy the climbing.