Charlene,
Regarding maps, I'm very partial to the Nat Geo Trails Illustrated Maps. They have one for all of Yosemite, #206. That one is O.K. for a total overview but not detailed enough for the hiking trails. This same map is broken down into four sectional maps more appropriate for backpacking. They are waterproof and tear resistant. They are called:
#306 Yosemite SW - Yosemite Valley & Wawona
#309 Yosemite SE - Ansel Adams Wilderness
#307 Yosemite NW - Hetch Hetchy Reservoir
#308 Yosemite NE - Toulumne Meadows & Hoover Wilderness
You can go to Nat Geo's website to get a closer look at these maps; just make sure you search the Trails Illustrated Map section.
The Other Tom presented some valid questions regarding hiking ability, experience at high altitudes, etc. that represent legitimate concerns. If you have never hiked at altitude the sometimes dry and rough trails in Yosemite can beat you up at 6-8 miles every day. As an older hiker I've often noted how easy it is to look at a trail map and say, "It's only 7 miles from here to here" but when I get out there with 30-lbs on my back that 7 miles can seem like 12! Also, if going in a group your top speed will be the slowest hiker, the one most susceptible to altitude sickness, blisters, fatigue, dehydration, whatever.
We often make the case for those who have never been to Yosemite to do the tourist thing first with lots of day hikes thrown in to get the lay of the land, a good dose of the trails without heavy packs, and enough introduction to provide a better idea where you would like to backpack on your return visit (there WILL be a return-you will find a way-we guarantee it).
If you are still dead set on backpacking from the get-go I highly recommend visiting the Nat'l Parks Yosemite website. You can get into the backpacking section by hitting "Things to Do" and then search deeper for things like trail permits, trail quotas, wilderness regulations, bear canister rentals, etc. There are many layers to this website. Note: 60% of trail permits are apportioned to advanced reservations (up to 180 days prior) and the most popular ones go very fast on the 180th day prior. The remaining 40% are first come first served walk-ins that require lots of flexibility on your part--particularly on weekends. If you go in without reserved permit please be kind to others waiting in line by being ready with a list of alternate choices without consuming lots of the ranger's time. Each trail has a daily quota for number of backpackers who can enter; there's no limit on day hikers. Trail quotas are in large part predetermined by the estimated daily impact on most likely camping areas, in other words, buried human waste and trampled grounds.
That's it for my advice. Others will provide more.
Jim
Edited 1 time(s). Last edit at 01/01/2015 09:34AM by tomdisco.