The Margaret River Signboard pretty much says it all.

http://www.surf-etiquette.com/text/Tribalaw.pdf

1) Furthest Out or WAITING LONGEST
2) Furthest Inside on the wave / closest to the peak
3) First to Feet
4) Call / Communicate (left or right, mine, etc - discuss that the next wave should be yours because you have been waiting a long time now..., or vice versa, next wave is not yours mate, as you just had the last one)
5) Don't drop in or snake
6) Paddle wide
7) Stay in the white water
8) Don't throw your board if it will endanger others

1,2&3 above will confuse some newcomers to the surf.....

If you can't surf your SUP board tight in the pocket, when other surfers are there doing just that, I'd suggest the SUP should paddle to a different wave.

SUP's should always consider other 'old school' surfers, especially at the classic point breaks.

Wait your turn, be patient, show respect.

If someone drops-in inside you, it is not necessarily snaking.... they might have been waiting longer, or are just closer to the peak, dropping into the wave when they can (after an SUP can pick it off). True snaking is deliberately paddling inside others who are waiting, in order to exercise the 'closest to peak rule' which is why this rule comes after 'waiting longest and furthest out'. SUP's should delete 'furthest out' and go with 'waiting longest'.

Here's some more;

www.surfinghandbook.com/knowledge/surfing-etiquette/
Link gives more definition. Below is high level summary

Rule #1: Right of Way - closest to the peak
Rule #2: Don't Drop In
Rule #3: Paddling Rules - take on the white wash, not the shoulder
Rule #4: Don't Ditch Your Board
Rule #5: Don't Snake
Rule #6: Beginners: don't paddle out to the middle of a packed lineup
Rule #7: Don't be a wave hog (TAKE NOTE SUP's!!!!!!)
Rule #8: Respect the beach
Rule #9: Drive responsibly
Rule #10: If you mess up - apologise

It doesn't matter what you ride, you must obey the basic rules of surfing. For Stand Up Paddlers who are new to surfing, you must realise you will be in the line-up with some crew who have been surfing for 20-30-40++ years. If you are in your 20's or 30's on a shiny new SUP Board, without good poise and balance, and with poor surfing technique, you will be noticed !!

If you are surfing on an SUP board, and have never heard of ALL of these following names, and do not know what era they were in their peak, then do some more homework before hitting the surf... the surfers are; The Duke, Dick Brewer, Robert August, Bob McTavish, Nat, Greenough, Billy Hamilton, Jock Sutherland, Gerry Lopez, MP, Wayne Lynch, MR, Curren & Carroll, Occy, Slater, Luke Egan, Mick Fanning, The Hobgoods, Joel Parkinson, Kekoa Bacalso (young Hawaiian Shredder), etc.

Trivia Question: Who would you consider the father of Australian Stand Up Paddle Surfing...
My Answer: Snowy McAlister. I understand he used to love surfing Fairy Bower in Sydney, standing up with a paddle, on a hollow pin tail finless board. Circa 1950's onwards...

Again, if this trivia is a total revelation to you, do some more homework before hitting the surf..... If you have never heard of The Bower / Fairy Bower, again, you need to do some more homework.

When surfing, remember to smile, and apologise if you stuff up, and if you stuff up twice, paddle in immediately !! Mick Fanning suggested it is difficult to punch someone who is smiling..... regarding being in foreign line-ups....

Simon