1. Basic strength training: You wouldn't expect to be able to finish a marathon on your first go, with no prior training, and that's on a flat surface with plenty of places to rest and no place to fall from. And climbing a big wall takes some strength, so you'll need to have a good core fitness program under your belt, including lots of dynamic and bodyweight exercises. After all, it's no fun to have to bail early on a climb because you're too weak to continue. This same core strength will serve you well on just about any adventure, so the time spent is well worth it.
2. Specialized skills training: Considering that you're not just out for a couple of hours on a sport climb, with bombproof belays and easy access to the ground, if you want to climb El Cap you'll want to put in some serious effort working on climbing-specific strengths and skills such as crack and crimp work, with an emphasis on sustained continuous efforts and keeping your body balanced and in control. Other types of adventures have sport-specific skills that can be practiced beforehand, either at home or with a ‘pro'.
3. Routefinding: With over 100 different routes to the top of El Cap, it's not as simple as just starting at the bottom and climbing upwards on the obvious path. You'll need to do some research to find routes that match your strengths and are at your skill level. Routefinding is a bit different off the rock, but still applies regardless of the type of adventure. Finding the most efficient (and practical) route from one place to another is a handy skill to have, from the city streets to the backcountry.
4. People skills: As with most climbing excursions, most of us will never solo up El Cap, so you're gonna need to have a partner for this climb. And not just a partner, but someone who also has the skills and attitude to make it to the top, and someone who you can spend a week alone with, without wanting to freak out on them. Your lives will be in each other's hands the entire climb, so the person you choose to climb with needs to be absolutely trustworthy for belaying, anchor placement, and other such climbing survival skills. If you do any sort of group activities, especially those which have an element of risk, being able to lead, follow, or facilitate is a great skill to have.
5. Hire a guide: Perhaps you've got the stamina and will to climb El Capitan, but not the hard skills of a big wall climber, but still want to attempt it, consider hiring a climbing guide to climb with you. Qualified climbing guides should have all the gear and skills to get you safely to the top of the crag, plus intimate knowledge of the routes and what it takes to top out on them. There are professional guides (or trainers) available for just about any sport, and paying a pro to lead you and instruct you at first is an excellent way to get a jump-start on your skills.
6. Traditional climbing gear placement: This is no local toprope crag, so you'll need a full rack (there are many recommendations for what to carry, depending on your route), plenty of ropes, knot skills, and the knowledge to use the gear correctly for protection. You and your partner will also need to know how to safely clean the gear behind you, as well as having a system for switching leads and setting up safe bivvy spots. These are not skills you want to learn while you're on the face of El Cap, so get out early and often and practice a lot before you think of attempting a big wall. While other adventure sports may not use climbing gear, they may have sport-specific gear or methods which you ought to be familiar with before you actually head out.
7. Aid climbing skills: Some routes require knowing how to ascend a fixed rope, or how to pendulum on your rope across to the next section, so knowing how to aid climb and set up safe places to rest and belay from are essential. Learning how to use the most practical aids to help you get through a rough section of whatever adventure you're on, before your life depends on it, is a wise thing to do.
8. Rappelling and downclimbing: Not every pitch will be successful for you on the first go, and not every adventure is completed easily, so be prepared with a plan (and the skills) to retreat from single pitches or the whole route. Be comfortable with the skills of downclimbing and setting up a rappel anchor, and consider taking a class on emergency assists and rescues if possible. For most adventures, you'll want to know the best way to ‘bail' or abort the attempt in the event that something goes awry, as even the best planned projects can get borked halfway through.
9. Packing and hauling gear: An average El Cap climb takes about a week, so you'll need to think about what you're going to eat and drink during the climb and be prepared to pack and haul it efficiently with you. You'll also need to carry gear for spending the nights on the wall, plus safety and emergency gear and changes of clothing. For faster and stronger climbers, a backpack may be possible, but for longer ascents, having a big haul bag to pull up behind you at each pitch will work much better. So you'll also need to know how to place secure anchors and set up a haul system just for your gear. Getting good at packing and carrying the gear you need for your adventures will pay off big time when you're out and about, whether you're on a bike, a boat, or a BASE jump.
10. Domestic skills: Some camping skills transfer over nicely to long hours on a wall, but other skills, such as mobile food preparation and cleaning, will definitely need to be dialed in order to get up El Cap with a minimum of problems. Imagine setting up camp for the night on something the size of a single cot, and then preparing and eating and cleaning up afterward on it, all without a single thing falling off or being misplaced. Then pretend you're several thousand feet in the air. No matter what type of adventure you're on, you'll probably need to eat and go to the bathroom and clean up at some point, so practicing those skills in a similar environment in advance will help your efficiency (and lower your stress levels while you're out).
11. Pick your timing carefully: Yosemite's known for its bluebird weather and sunny days, but is also equally well known for the possibilities of storms and extreme weather at just about any time of year. Consider your own preferred climbing temperatures and tolerance for company when planning your climb, as some times of the year, the walls are swarming with other climbers, and yet other times are empty of climbers but hotter than the dickens. There's an optimum time for every activity and location, so do the research and talk to those who've done them before you actually set a date and time for your next big adventure.
Taking on a big wall like El Capitan is not a feat to be taken lightly, but with some careful attention to being prepared in your body, mind, and gear beforehand, it could be the trip of a lifetime. And those same skills can help you on many types of adventures.
[Images: tpuyol, mariachily]