Many recommend tight/aggressive for newbies to the game in an MTT. Also early in any MTT. Tight-Passive, IMO, can get you run over if anyone with half a brain catches on. They will simply bluff you left and right. Honestly, if you only play "big" cards (AK/AA/KK/QQ/KQ/AQ) people will pick up on this...real quick. They will simply bet big on any flop without big cards you are in, because they know you do not have any of it!
You also need to quickly learn how to shift gears. And I would shift from Tight/aggressive to loose/aggressive. Occasionally open up or call with a suited connector; this makes you more unpredictable. You sit there and fold 20 hands then raise one hand, they will all know what range you have. You have to get value for your hands and it is hard if they know you are playing like a rock or a nit.
If you play passive at all, do it after you get comfortable with the two aggressive styles. That will make you even more unpredictable. Then break out the occasional bluff. Pretty soon they just have no clue if you have the nuts or total air. That is the whole idea.
In other words, do not stick to any one style for an entire game.