I did this from the get-go and the long run has really paid off for me.
Started with immediately forming a team as a medic with a few semi-experienced chaps and went on from there. Learned so much through my teammates and I couldn't ask for more than playing with some really awesome peeps. Did a few pugs and enjoyed it but I do digress on how tf2mix sorta changed from the last time I played in it. Tons of complaining and felt that the newcomers were getting a bit too much heat.
DM and MGE are fantastic if you want to improve on your one-on-one and gamesense skills. Power Pugs and similiar groups can provide a more relax environment for pugging imo. TF2Lobby... ugh, I can say that if you don't come across trolls who has a mic, it's a way to improve on your comms.
But erm, enough about that. Definitely chill in Newbie Mixes and Power Pugs, you can meet some cool peeps and possibly find a team. And do UGC if you want to join a team to start building your competitive experience and relationships with peeps.
Psssst, hope you'll come to love TF2 tons. <3 Like me.