Pre-TournamentThe run up to an event can be just as important as the event itself and a lot of the time its something that gets overlooked. The majority of us don't throw together an army at the last minute and simply turn up to play and for the most part you will spend days / weeks agonising over which list to bring.
Always, always, read the rules pack before attending an event. I've done it in the past where you skim through a 5 page document and simply pick up on the points total and start writing a list but many tournaments now are putting their own restrictions on how many detachments, allies, type of allies, forgeworld and a whole raft of other considerations. There is nothing worse than finding out the day before an event that you can't take the list you wanted because of some of the restrictions in place.
Along side the rules pack make sure you check which (if any) FAQ they are using as this can drastically change your army if something is played a different way to what you are used to. Missions can also play a big part in how you construct your army so make sure that you understand the missions in the rules pack and any twists that maybe event specific. I've been to a number of tournaments where a custom mission was created for the event and when I arrived at the table found that my list was in no way suited to those missions.
Painting and army listFor me personally I use this time as an excuse to get something painted specific for an event. It helps keep me motivated when I have a deadline to finish off that unit or to try out something new. Even if its just switching out 100 points from one unit to another it can help to get your army finished off.
Some events will allow you to use unpainted models or even to proxy a few models / units. Try to avoid this where possible! For a lot of people one of the main attractions of a tournament is to see all the armies on display and to find inspiration for their own stuff, whether that is from a painting, modelling or even just list ideas. Either way, no one wants to attend a tournament and place their lovingly painted miniatures on the table opposite a wall of grey plastic.
When using proxies I have seen this escalate into a verbal slanging match between players because despite how many times you tell your opponent that this guy with a las gun is actually carrying a melta gun we will all forget. We look across the table to asses threats and just see the las gun. Of course this isn't a exactly a hard rule and most of the time common sense can be used. If you want to use this special character as a captain instead of the named guy it usually isn't that bad but using a rhino as a land raider can cause issues.
Its dangerous to go alone....
Know your stuff
While most of us will know our armies inside out make sure you check your list prior to the event and double check all the special rules and abilities they may have. The number of times I've played a game and on turn 5 someone remembers this guy has feel no pain or can re-roll to hit have been beyond counting. Its always a good idea to try and remember certain things that you know will come up such as how many attacks my assault unit has. You know you will try to assault with them at some point so you may as well double check the stats before you arrive rather than at the table.
At The Table
So you have arrived at the tournament and are standing across the table from your first opponent...
This may seem like an obvious one but a lot of the time I've walked up to the table and the first thing my opponent has said is "oh necrons is it...what's that do?" and we end up diving straight into lists, missions and rolling for deployment. Its a shame but most of the people I play get designated as Eldar Guy or Blob Guard List rather than their actual names. It also makes it more awkward when you play them again at another tournament. There is one guy I see at every tournament, have played him half a dozen times and still have no clue what his actual name is. Asking at this point is clearly out of the question....
Going through lists
Take the time to walk your opponent through your list, what each unit does and any special rules they may have. While this doesn't mean you need to give them the full stat line for every single model you have brought to the table it helps to quickly run through what they can expect. This unit has 2 melta's, can deep strike and has furious charge is usually enough but expand on something's should you need to.
Also, don't be afraid to ask your opponent questions about their list if its something you have not seen before. There is nothing worse than lining up all of your ap2 shots to kill a unit only to find out that it has a 2+ re-rollable cover save.
One of the things that catch a lot of people out at tournaments is the time limits placed on rounds. This is obviously a necessary evil as the results need to be calculated and the next round drawn. For those not used to tournaments playing a game with your mates over a 5 hour drinking session is fine but in tournaments you need to make sure its a fair game. No one likes having to call a game at the end of turn 3 because you ran out of time and this can leave people with negative thoughts about the whole thing.
Some of the things you can do to help speed up your games are make the roles and then check the stats. What I mean by this is if you can't quite remember if the leadership for this squad is 7 or 8 roll the dice anyway and then check the codex if its relevant. If you roll 12 you have failed regardless, if you roll 3 you have passed and you can check afterwards rather than your opponent waiting for you to look through a book. If you can't remember if this weapon causes pinning or not take the test anyway and check after. Things like running in the movement phase can also help speed things up if you check with your opponent first. On turn 5 I've often said to my opponent "I'm going to run these guys for linebreaker, do you mind if I run them now?" and then carried on with my movement phase for the rest of the army.
We all have those funny stories about how your lowly infantry sergeant killed drago in overwatch with a grenade or how you failed that 3" charge that would have won you the game and most opponents like hearing these stories but if you're telling one of these stories make sure it doesn't hold up the game while doing so. Tell it during the movement phase while you're picking up models or doing something else rather than stopping play.
Measuring things before you do something is a thing. It should be used as often as possible. Most of this can also be used in the time management section above to help speed up the game and stop any potential arguments before they arise. During your movement phase if you know you are going to assault something measure the full distance before you touch the model. Check with your opponent first how far away it is so that you both know what is required. If you measure 13" and know you can move 6" tell your opponent "So, I would need a 7 inch charge". This helps clarify it when you roll the dice later and can't quite see if its 7 or 8 needed. By agreeing with your opponent before hand you both know what to expect.
In a tournament setting this can be tricky when you or your opponent forget to do something. 90% of the time I will allow someone to go back and do something but you have to remember that you are in a tournament and sometimes the best way make sure its not forgotten the next time is to make them suffer for it. This may sound a little harsh and its often hard to say no at some point but I have played a game at a tournament where my opponent forgot he had some psychic powers until turn 4 and then asked if he could roll his powers now. Going back a couple of steps isn't big but going back 4 turns can be a bit much. If you forget to do something point it out to your opponent but don't expect them to allow you to do it anyway. A lot of the time I will point it out and then refuse to do it anyway until next turn (it will not die is one that immediately comes to mind...).
Also consider how import it actually is in the grand scheme of things. I've had an opponent forget his psychic phase completely and go back to it only to cast guide on something that ended up moving flat out and not making use of it....
Don't Give Up
You're at a tournament and could be vastly outmatched in terms of mission, army composition or indeed by the player themselves but remember you are at a tournament. Giving up at turn 3 may seem like its the only option left to you but you maybe able to squeeze out a couple of tournament points by the end of the game which will effect everyone else's results. I've seen tournaments be decided by VP difference at the end of 5 games and even then there is only 1-2 points between first and second place. If you allow your opponent to take a full 20-0 victory it can have a huge impact in the final standing than if you played it out and simply lost 18-2.
It also becomes visible to your opponent if you are not enjoying the game and can suck the enjoyment out of it for them as well. I think we have all played that one game where our opponent looked downright miserable and both of you are simply wishing for the game to end. Even if it looks like you have no way of winning the game set yourself a goal to try and achieve. It may just be to get linebreaker or to make sure this one scout survives but it helps to keep it interesting.
The most important rule
Whether you go to a tournament to try and make a podium finish or just to have a weekend of playing 40k always remember to shake hands with your opponents before and after a game and make sure that both of you are having an enjoyable game.