My Ten don'ts:
1. Don't take product advice from someone who has never used or owned said product. Most often noticed in locker discussions.
2. Don't buy a winch without having $3000 in your pocket. Winch is pretty useless without all the support equipment. Gloves, mount, batteries, hilift jack, shovel, another shovel, 4x4 wood boards or ramps, snatch block, shackles, more cable/rope. Seen too many people who can only afford the winch, and skimp on good exposion proof shackles. Usually the same newbs who don't hang anything on the cable.
3. Wheels bigger than 18"
4. Lifts too high, and or tires too big.
5. Big tires, little gears.
6. Too many lights pointing forward. None pointing sideways, none pointing rearwards, none under the hood.
7. Snorkle, but no raised fuel tank vents, axle vents, trans vents.
8. Cheap rocker armor will just increase the damage your truck recieves at the rockers, use strong rocker armor if you need it, not cheapo bolt on garbage. (Unless your particular trucks bolt on stuff is strong enough, I've only seen welded on custom jobs that could support the weight.
9. Huge Yakima baskets. Ladder racks are alot cheaper and sturdier.
10. Wrong tires for application.
Some comments after reading this thread:
-learning about ham radios is a nightmare. The internet just sends a newb running in circles. Most ham forums can't answer the simplest questions. "Can I use a ham to talk to CB users?" "Exactly where do I go to get licensed?" "Can someone give an exact list of a good starting setup under $1000?" "What type of mobile antennaes can I use?" "Does John Wayne like beans in his chili?"
I'll stick with CB's for now. And who deosn't have a linear these days? Allthough when using two good radios and our cell phones for testing. If our radios were really good, custom tuned Galaxy etc. etc., we noticed allmost no increase in range or clear reception with the linear amps on. Usually the radio started to drop off at nearly the same range for all practical purposes as a well setup stock radio with a big whip.
Plenty of truck drivers have called my radio a nice "ham" after a radio check. It's not, it's just setup correctly. I also like Wilson and long whip antennaes.
-good lord I'm sick of diamond plate
-diesel stacks are great for covering your entire truck bed in messy carbon. So much for keeping gear or bikes in the bed. it would be impossible to go on a single expo trip without looking like a coal miner.
-Winches are scary. Why do people assume that because they have a winch that they don't need a shovel, ramps/boards, or hilift anymore? A snapped cable is worse than an angry Chimp with an AK47. Especially fullsize trucks that can really vacuum themselfs to the bottom of a mudhole. I love youtube vids of people ripping off another truck axle from improper winching. Also, I never have any trees or rocks capable of holding up to winch forces nearby. Usually just small trees. Getting the hilift jack out to get stuff under my tires is quicker than burying my spare wheel for a winch anchor. Sometimes a little time spent with a shovel can be the difference between tugging with 5000 pounds of force on your line, and 10,000. I'd rather not max out the potential energy of a 15,000 pound winch ever. It would be safer to paint a grenade neon green like a tennis ball and let my golden retriever paly with it around the camp fire.
-I disagree about armor. I love it, but can't afford the good stuff, so I use it sparingly under my tank. But if you can afford the good stuff, more power to you. I've seen some Road Armor and Fab Fours bumpers take some huge hits. I think the frame would bend before some of those bumpers. I'd love a Road Armor front bumper, we have 10 times more deer in my area than the Auzzies have roo's. I see one run across my path 3 times a week this time of year.
-I like mild lifts so I can cross a road side ditch. But other than that, usually a 1" spacer in the front of a pickup, decent tires, and a Detroit locker in the rear will get me just about anywhere. It rare for me to recommend anything over 3-4" of lift.
-I love Hilift jacks and the wheel strap tool. I just jack up by the wheel and stuff some wood under. I also use it to lift trailers up to my hitch when one of my other field techs parked that trailer in a way that I can't get the trailer jack low or high enough to hitch up. problem solved in 1 minute with a hilift. And when one of my work trucks gets stuck in a field. It's usually only stuck 2" deep. I can jack up off my hitch, thenjust shove the truck over and let the jack kick out. Do that a couple times, and I'm over onto a harder patch of earth and can drive away.
). It used to be that we place a 2M rig at waist and tail and they could relay start to finish. It wasn't nearly the issue this time and I think as years go on more will invest in the system. 
