This is my 5th year going and here are all the things I learned, some the hard way...
1) Get there at the right time!
It seems obvious but know your store and know how many people to expect. Best Buy usually has a LOT of people -- OfficeMax and Staples, not as many. I got to Staples about 90 mins before open and I was literally the first in line, yet at Best Buy people got there 4-5 hours before open.
2) Know your store! A lot of times larger stores will give out maps to sections and even big-ticket items, but you can't count on it. Go to your store on Wednesday (many are closed on Thursday) and make sure you know where the sections you'll need are located. Don't forget to keep your eyes peeled to the floor displays regardless of how well you know the store, many times big ticket items are placed out on pallets on the aisles, away from their department.
3) If you live pretty much anywhere but the deep south you'll have to dress very warmly. Take off your extra layers BEFORE going in.
Most stores are kept to a moderate temperature and you will be VERY uncomfortable waiting in line-- not to mention winter gloves and coats don't make you very maneuverable through the crowds. Park close to the store if possible so that you can throw your coat/gloves/hat in your car before going in-- have a friend save your spot in line (more on that in #4) but if that's not possible, usually a person in line will gladly save your spot.
4) Bring a friend! The advantages to this are endless. A friend can save your spot in line while you go to your car, see #3. One can grab some snacks while the other waits in line-- especially in large stores like Best Buy. And of course the obvious advantage-- splitting up! One friend can get some items (duplicates of course) while you get others.
4.5) Related to #4, charge your cell phone the night before, so you can meet up with your friend easily.
5) Make a list of the items you are going to buy. You can spend all the time in the world concentrating on the big items, and forget the small, cheap ones and remember just as you walk out...
6) Don't bother packing your iPod, your Game Boy, your PDA, a deck of cards, your Family Guy DVDs, your dog, your personal trainer...you get the idea. Don't worry about being entertained while waiting in line. You're almost always going to find someone to talk to and your extra gadgets are just going to add extra bulk. Anyone who is standing outside an electronics store at 4 in the morning when it's 25 degrees out is probably into computers and electronics just like you, so strike up a conversation.
7) On rebates and picking items/stores...seriously, just think about how much your time is worth. I'm not saying rebates are a scam, but seriously, if one item is $5 cheaper and has 3 rebates, go with the item that is $5 more and has one rebate, or better yet, Staples Easy Rebates (they really are easy). If it's a big difference, yeah, go for the extra rebates, but if it's $5 or $10...dont' waste your time. You'll thank me later.
7.5) Check prices online before you get an item. Often times I've found that regular, no rebate prices on Newegg, et al, are not much more/same as the BF prices. Read product reviews too! I've bought many a crappy product at BF *coughlexmarkprinterscough*
8) Don't bother hiding items the day before. Seriously, don't waste your time. I know people who work at Best Buy, Staples, et al, and it just doesn't work.
9) This one might surprise a lot of you, but go for the less popular items first!
The big front-page specials, stores know that a lot of people are going to go for them, and they're probably going to keep a lot on hand. Other items, maybe not as many, so worry about those first, then go for the big stuff. I remember in 2003 at Best Buy, I got there at 9:30 (my dad had been waiting in line, I had been to Staples and OfficeMax) to meet him in line and lo and behold, there were DVD players and hard drives still in stock! The smaller, less popular items on the other hand (not the FAR stuff!) were all long-gone.
I think that's about it for now