by AlmostThere » Thu Jun 24, 2010 10:21 am
Go to the official Yosemite website and look at the trail descriptions, trailhead quotas, and all the wilderness regulations. You will need to use proper food storage and know how to dig a hole to relieve yourself, and to pack out used TP per regulation. (Pay very close attention to the food storage page and the bear canisters they approve - YOU MUST USE one of the approved canisters. You cannot hang food. You will lose it and risk a fine.)
Pick up some maps - Tom Harrison maps are good. Get one for the area of the park you think you might want to visit, not one of those huge park inclusive ones that make it hard for you to estimate mileage and navigate. (You should have basic map/compass skills. I know people go out without them all the time, but you should have them. The Search and Rescue teams will thank you.)
Get the maps after you pick up one of the numerous guide books on Yosemite hikes and read some trip descriptions. I like Sierra North, it also helps to explore areas around the park as well as having many good hike itineraries inside the park.
If you have never backpacked before, get your gear together and take it out somewhere local to you overnight to test it out in the field and get the bugs shaken out. I recommend the articles and gear lists at backpacking.net as a starting point.