I hike here nearly every weekend. It never gets boring. Summers are pretty hot, so plan to start early, like at 5am. Springtime is always gorgeous, the wildflowers and cactus are in full bloom and everything is green.
Lots of people hit the trails with their dogs, but if you take yours please bring bags to pick up after your pooch. Those who don't are LAME. Try to keep your dogs leashed also. I have a smaller dog but some people are terrified of any dog (I've run across a few of them) so please follow the leash laws. Bring water for your pets too - some friends of mine saw a puppy die one summer because the owner didn't bring any water.
There are lots of great trails here. The Mormon Loop is really popular. It winds around and has some good rigorous uphill areas. The Ridgeline is great too but avoid it if you are afraid of heights.
There are different ways to access the park, so be sure to check it out online to pick the right one. (I tend to go there by way of 48th Street near the I10.)
Tips:
Dogs are allowed (but must be leashed)
Bring lots of water (for your pets too)
Bring an energy bar or two
Bring tweezers in case you accidentally step on or touch a cactus
Bring your cell phone
Bring a whistle in case you get injured or lost and need to direct people where to find you
Wear the right shoes! One time I saw a Brownie troop, some of them wearing flip-flops. There were about 45 mins in, looking miserable. Hiking boots, sturdy sneakers etc. are appropriate.
Watch out for mountain-bikers. Stay on the right side of the trail.
Don't litter!
More tips, including nude hiking (??!!) can be found here:
http://www.abc-of-hiking.com/hiking-etiquette/hiking-etiquette.asp
Enjoy and have fun!