1. Wear sunblock, as well as chapstick with SPF or your lips WILL burn.
2. Drink water and then more water.
3. Wear the comfiest shoes you can find. Closed-toe shoes are essential if you're going to try to get near the front of the stages at night, so your feet don't get stepped on.
4. Choose the right clothing: light clothing during the day, and bring long sleeves at night. (It's a desert, it can get a little chilly for some.)
5. Arrive in a good mood, this is going to be a good weekend for you.
6. Book your hotel or camping spot early. Sleeping options can often sell out more quickly than tickets.
7. Shower (please for the love of god). Your neighbors in the crowd will thank you.
8. Eat and take a break. Sit down.
9. Save drinking large amounts of alcohol till afterwards, because the sun will kill/drain you.
10. It's smart to buy the t shirts/merch you want early. They often sell out at night and the lines are very long. Locker rentals are available to keep stuff in during the day (but don't leave vinyl because it will melt).
11. Expect to wait in the morning at the entrance gate in long slow moving lines. Either arrive way early or relax and take your time.
12. Don't be a scarface and try to smuggle crazy ass drugs in there. While relatively lax, security/police do escort people out from time to time, and that would be a bummer of a weekend for you.
13. Don't "push your way" up front. This is kinda important. If there is an artist you want to see, get to that stage while the artist before is still on and just wait it out, you just may end up see something else you like too. In other words, don't be the asshole.
14. Have a physical meeting spot with your party, because your cell phone reception is spotty at best.
15. Bring sunglasses.
16. Know that you WILL miss some acts you wanna see. But do move around to the different stages and see as much as possible.
17. Expect LOTS of traffic to and from festival grounds. Have patience.
18. Buy your 3 day pass as early as you can. Coachella has sold out in the past, but not every year. Board mod Psychic Friend usually gives a warning of sorts somewhere in the message board, if things are getting close.
19. Don't lose your digital camera. In case you do lose it, to help the good folks at lost and found, you can take a photo of your contact information and have it on the camera... it could be you holding up a sign with your phone number, email, whatever.
20. Don't forget condoms.
21. Limit your time in the beer gardens. They are well away from the stages and over-priced, and you will be missing out on a ton of musical fun.
22. Get sleep.
23. Print out a set times schedule and keep it in your pocket, or save the schedule on your phone. Circle or highlight the bands you want to see so that you don't forget. (They will have printed schedules there, but sometimes it's difficult to find them so it's better to just already have one.)
24. Plan any of your tent signings early, and prepare to wait for your favorite, but don't go nuts at the signing tent, you'll miss lots of music. Artists and the signing tent run way late and there are always cancellations throughout the day.
25. Bring more cash than you think you will need.
26. When possible, don't wear a backpack. Especially in the crowds near any stage. Unless you are working, you should leave it at the hotel, tent, or even a locker. The person behind you will be glad you don't bump them every time you decide to dance a little. Plus, it's one more security check you'll have to do.
27. Hats might be a good idea for sun protection, but don't wear something obnoxiously big that will block the view for those behind you.
28. NEVER text "Where are you?" or any text that requires a response because by the time you get one, your friend won't be where they said they'd be. Text affirmative statements such as "Meet at Sahara Tent at 6:30pm" or "Meet in beer garden by main stage at 8pm". Finally, time stamp your texts because ambiguous times like "Meet me in 20 minutes" doesn't mean a damn thing.
29. Give yourself enough time to go from one side of the Polo Grounds to the other. It's a bigger area than you think, especially if you're going from the VIP or Main Stage area to the Sahara tent.
30. If you choose to write on cars in the parking lot - please - keep it on the glass, the dust will scratch most paint. You and your friends can still marvel at your jr high bathroom drawings without doing any damage to someone's car. It's a win-win.
31. Consider bringing something for chafing. You'll be doing a lot of walking around. Try Goldbond body powder, Chamois Butt'r, Monistat anti-chafing cream, or Bodyglide sticks (runners use them). Lots of men like using underarmor or other brand compression underwear. (Tip credit: PlayaDelWes, JustSteve and weeklymix)
32. Bring supplies for the portopotties: hand sanitizer, wet wipes, seat covers, p-mates for the ladies, and toilet paper can all be lifesavers because the portopoties will likely run out of supplies early in the day. (Tip credit: jlandgren and koryp)
33. If you have glasses, bring both extra contacts and contact solution as well as eye glasses. The desert air is super drying. (Tip credit: Ha.SK)
34. Bring earplugs. Your ears will thank you when you're standing right next to the speaker of an especially loud set.
35. Ibuprofen can be a lifesaver for muscle aches, accidental sunburn, or headaches.
36. Baby wipes or face wipes can help to keep you refreshed, especially to wipe off sunscreen, sweat and grime when the sun sets. (Tip credit: ivankay and whynotsmile99)
37. The toilet trailers have flushable toilets and are air conditioned.
38. If you have allergies of any kind, bring Benadryl/Claritin/Sudafed. All the dry grass and dust in the air can be a killer. (Tip credit: lizng and The Dude)
39. Consider bringing a way to recharge your cell phone. Having to constantly search for a signal will drain your battery quickly. Turn off 3G/4G/Bluetooth/Wifi unless you really need it, to save your battery. There are usually tents that offer recharging stations, but that's time taken away from listening to good music.
40. Fanny packs are super convenient for carrying stuff without getting in the way. (Tip credit: ashleysmashley and amyzzz)
41. Consider using a car finder app on your phone, or making a point of writing down directions to your car. You'd be surprised how easy it is to forget after 12 hours. (Tip credit: baily)
42. Make sure to bring any medications in their original bottles. Otherwise, security will confiscate it. (Tip credit: ChristinaStelly)
***Credit goes to CDUB for this whole post. Thanks CDUB!***