My quick start guide to competitive demoman 6v6

This is mostly talking about vanilla TF2 because the demoman's new weapons are not particularly competitive - and I prefer playing vanilla.

Either way this guide will give you a basics for instant improvement as a newbie

For the more advanced -
This guide talks about EU style Demoman - American teams usually place less emphisis on the demo and more on the soldiers, whereas us EU players tend to like the sudden destructive force and volatility of an uber-charged demo

So then.

Basics.

unpredictability

this against soldiers and demos and the like, is an essential skill for any character to have. most people can strafe side to side, but intermediate players can always be recognized by their poor strafing skills. It is difficult but you cannot simply move side to side predictably or constant strafe around someone. because you are going to get fragged by a direct shot. basically just avoid the kind of movement that makes it easy for them to hit you obviously.

but vary your timing, make your strafes short and move outward if your opponent is aiming narrow.

Scouts

your worst nightmare.

the best defense is your sticky launcher - by using area denail which I will explain below -
however if the scout is close up you will either need to use your pipe launcher - this will be difficult at first - or if they are taking the piss then use the bottle

but this is a last resort because if you have let a scout get that close and are not quick to use a pipe the chances are you've died already

 Right and now into gameplay 

STARTING 
I'm not going to waste my time talking about sticky jumping because this skill can be found anywhere, all I will say is that before the clock starts you can get yourself closer to the door with a sticky jump - and you are also the most mobile class - it is perfectly possible for you to reach the middle of a map long before the first scout does - using your sticky jumps. but you will have to be accurate and get the right force behind you - but use your jumps to race to the center - without taking too much HP - and right away lay traps in case of enemy demos and/or scouts - this could gain you an early lead if done correctly


Area Denial
Use the sticky launcher

THIS IS YOUR PRIMARY WEAPON


It doesn't matter if someone calls you a noob for using it all the time in pub servers - this is how competitive demo is played.
so basically this involves placing sticky bombs strategically so that your enemies dare not tread near for fear of being fatally maimed
You should be making them feel like this a lot - especially on ground that your team needs; It's one of the only ways your team can hold a forward position - so you ARE THE GUY, don't waste your ammo by detonating too soon or too much.


TRAPS
I can't stress enough how underused this is. traps used to be extremely common practice until people got wise to the basics - the basics being look out and be careful when going round corners - especially if a demo is in sight.
however no one uses quick spontaneous traps - and this is something you will have to remind yourself to do until you are used to it, the best way of causing maximum damage when your team is on the run is to run round a corner and place a mass trap - if they are just pressing on with their team and riding on the high of winning, and believe me this happens a lot, then quite often they will not think that you may counter attack in the blink of an eye. so don't waste time placing traps unless you are fairly sure they are going to have an effect - because other wise you are wasting ammo you could be using for area denial.

NOTE - the easiest way of getting through an enemies defenses is to kill their demoman. This removes all of their sticky bombs that are placed
this means you will have to be able to handle the enemy scouts as a team because they are coming for you
you should be denying them the ground and your team should always have priority on saving the medic and then you.

SplashSplashSplash
splash damage is extremely god for your team - as most teams inevitably end up bunching up at some point by accident or through a door etc. your sticky bombs are the perfect weapon if your team is prepared to unload some DPS on the enemy team and this lead me to my next point

you can also use your pipe as intelligent spam - try to keep the enemy under pressure with this

The reason we take the ubercharge
this allows us to know exactly what the enemy is going to do - firstly the medic is obviously going to be target number one - so PROTECT HIM
let me also note that this works with the kritzkreig aswell as the ubercharger
you have massive potential for continuous burst AOE damage - so when you have kritz or uber - the enemy team will be terrified of you. they will pull back quickly so try and pop the uber suddenly and take the enemy by surprise and you will pave why to wipe their team

remember your priorities - MEDIC, SCOUTS
once their medic is down the scouts will gun for you so grab them before the charge runs out but let me reiterate the medic is the key
without their medic they are doomed

Airshots & Accuracy
even an experienced demoman will still use the sticky launcher more as it is simply more tactical - however when you get pro at using the pipe launcher - this is the most powerful weapon in the game - so you need to be able to airshot scouts effectively - this is really your ultimate goal. once you can do this like a pro the rest will fall into place, but remember to always think about what you are doing -

know when to run away
again this is overlooked but this separates the newbies from the intermediates - don't get cocky and your K/D will serve you well

if you are on a public server and your K/D is less than 4:1 you are doing something very wrong - read again - be aware of other classes capabilities and basic play.

Communication
the most important factor in your team play - the medic is the boss in most situations they take the role of team leader.


Lastly
Watch frag videos - I can't give you the best idea of how to play simply from this but frag videos you can see subtlteys and little tricks that really improve play or that are for pros

disclaimer - this is not my video it is simply an example (search youtube for more)

e.g. tip trick - as a soldier or demo you can use the rocket launcher or sticky bombs to launch dropped weaponry and hence: ammo towards your character - this can save you time in tight situations