When players come to play their first competitive REL event, what are the most common mistakes they make and the most common infractions they get? Which ones would be the most important to mention in the opening speech to prevent them from happening?

Maybe there have articles written about this as well, either for judges or for the players themselves, I'd like to see those too.

Thanks =)

Off the top of my head:

1) Remember your triggers. (I know technically this applies at Regular, but it's even more important at comp.)
2) No take-backsies.
3) Don't be late for your round.
4) Return your deck to its original state for the first game of every match.
5) General reminder that players will be held to a higher standard for accurate play.
6) If something goes wrong call a judge right away, don't try to fix it yourself.

Edit:
7) Have fun! This is a serious competitive event. But most of us aren't doing this for a living. So don't forget to have fun!

Edited Adam Zakreski (Sept. 1, 2013 10:14:47 PM)

1) Decklist.
* If limited, write Your name, Basic Lands. Please count 40. Then, please count 40 again.
* If constructed, write Your name. Please count 60. please count 15. Please count 60 and 15 again.
2) Judge call is not bad thing.
* If you have something wrong, please call judge immediately. When you don't know you should call judge or not, please call them.
* Don't fix your game only by yourself.

Don't roll a die or use any outside the game method to determine the result of a game/match.

Biggest mistake from personal experience? Believing that calling a judge is a dick move. No. Call a judge! Also communication - not a mistake per se but very underused when transitioning from the kitchen table or FNM to a PTQ.

- Jack.

Originally posted by Kenji Suzuki:

1) Decklist.
* If limited, write Your name, Basic Lands. Please count 40. Then, please count 40 again.
* If constructed, write Your name. Please count 60. please count 15. Please count 60 and 15 again.
2) Judge call is not bad thing.
* If you have something wrong, please call judge immediately. When you don't know you should call judge or not, please call them.
* Don't fix your game only by yourself.

By far these are the two I most commonly give out infractions for.

Adam's list is a very good HJ tournament reminder speech, although I would definitely add in something about double (triple!) checking your list for name(dci)/count/sideboard.

Like the video says

ASK A JUDGE!
www.youtube.com/watch?v=fiakR7NgtF0

lol

I wrote this article a while back aimed at players that are moving up from
FNM to Competitive REL. :) I don't think that anything in the article has
been outdated by IPG changes.

http://legitmtg.com/competitive/making-the-move-from-fnm-to-competitive-events/

-George FitzGerald
L2, Sarasota, FL

Originally posted by George FitzGerald:

I wrote this article a while back aimed at players that are moving up from
FNM to Competitive REL. :) I don't think that anything in the article has
been outdated by IPG changes.

http://legitmtg.com/competitive/making-the-move-from-fnm-to-competitive-events/

-George FitzGerald
L2, Sarasota, FL

Thanks, good read =D
The part about sideboards is outdated, that you are not allowed to have a 14-card sideboard and that you are not allowed to side in 5 cards but only take 4 out.