You've already gotten some great advice but as mostly a desert hiker I can pass along what I do...
1. my shirt is usually a white, cotton/poly blend, long sleeve dress shirt. A cheap one, thin, washed a bunch of times. They are cool and reflective, and offer protection from sun and wind. Easily washed and dried.
2. I like really light flimsy convertible pants. Zip off the legs in daytime, back on when things cool down. The shorts need to be knee length. Underwear will be really light competition running shorts, nylon. No cotton here.
3. Trail runners work best for me unless I'm headed out across the desert floor, off trail, then light boots, leather. Socks are always super thin, cheap, nylon, walmart versions. Worn two pair at a time they are still thinner than normal socks and combined with Bodyglide, blisters simply won't happen.
4. BRING PROTABLE SHADE!!! I hike with a lightened umbrella in the desert. You will stay cool,cut water consumption, keep energy levels high, watch your friends sweat, lots of benefits. Bring a light poncho shelter, mylar space blanket...something to get out of the sun and rest. The desert almost killed me once and this is the biggest lesson I can pass along. Shade.
5. At least one trekking pole (i like converted ski poles...stronger) for hiking of course but also for lifting the odd cactus/prickly/bush out of the way.
6. Water...plan to haul double your needs with a reserve. It depends on where you are going so plan well and cache some if at all possible beforehand. I use platypus bags...easy to pack. Water will be half or more of your pack weight.
7. Hat/bandanna. Big hat that will cover your neck. The dress shirt will have a collar that you can keep up as well. A half day of desert sun exposure can ruin your trip, and your skin.

Enjoy your trip!