playcomp.tf

Find a class you really like and really want to learn. Stick with that class and learn how to play it learn your character in and out, know your limits with your main and enjoy playing it. Like what jnki posted, that's a great place to understand the basic format of 6's and know what classes are ran. Also once you find the class you want to play try to find videos, POV demos or a solid mentor to help you understand 6's.

Playing matchmaking as it is right now is not a good way to get into competitive 6s but I'm going to add you anyway since I have some leftover beta invites.
If I were you I'd go to tf2center and start playing highlander lobbies as scout. There you're not a very important class so people won't get mad at you if you don't do well and it's a good way to see what your skill level is at compared to the tf2center community. If you do alright in a couple lobbies I suggest you move on to 6s and play a not very important class there (such as roamer or scout). If you do alright there you should play the class you want to main in 6s lobbies and get as good as possible at it. You'll make friends from tf2center and you can join or start a team with them. That's how it went for me. You can also add people from ozfortress, the Australian tf2 league who are looking for players and ask to trial (try out) for them. Etf2l has a recruitment page where people can post when they're looking for players or teams but I couldn't find that on ozfortress. It should be there if you look hard enough.

Also play a lot of MGE and DM. If you wanna be a medic main it's not neccesary but still very useful. Good luck!

Also check this thread. A good collection of guides and videos for 6s in general and for every class.

Shpee basically covered it all. The thing with matchmaking is:

• It is first to 2
  
• There is no whitelist (some broken / op weapons are banned in all leagues such as reserve shooter)
  
• There is no meta set in stone in MM which means you can't practice proper 6s (e.g. you could have a full time pyro which is never seen in 6s)

The skill in mm is probably very variable as you could see gibuses etc which would not mean proper practice. Jump in on tf2center and read a few guides before playing, and I'm sure you could fit right in!

Be sure to join Newbie Mixes on friday nights. They will help you get a sense of 6s. https://steamcommunity.com/groups/na6v6newbiemix

Hi Shpeeisme, i was actually looking at being a medic main (since i can't hit a shot to save my life) and i've done a bit of research too. i've watched shade do some demo reviews of other medic mains and also some youtube guides by Slin. from this, i've learnt heal order, and how to use ubers properly. i'm not sure what MGE and DMs are though (relatively new here if you couldn't already tell :P) but i'll do some research.

Anyway, thanks for the positive feedback!

Hi Squeeble, unfortunatly, various commitments mean that i can't join those pugs, because they are at 10:30am on a saturday for me. also i imagine that the ping would be almost unberable connecting from australia.

thanks anyway though, i really appreciate it.

I've added you, I can give you a list of useful aus servers and explain how competitive is run down here. The advice you'd get on tftv is usually na or euro-centric, so while it's helpful it's not always exactly correct or relevant to australian players. Also, I wouldn't lock yourself into being a medic main just yet, it's a rare player who can do well on combat classes with 200 hours in the game.

squeeble look at his flag he's obviously strayan why are you recommending him na newbie mix.
Also MGE is short for my gaming edge mod, it's a 1v1 battle mod used on MGE servers. DM is short for deathmatch mod, it's instant respawn deathmatch just as the name suggests. Since you're playing medic you won't need any of those because medic takes no skill. So just watch videos, play lobbies, play pugs, offer to be a ringer/substitute for a noob team.