I am about to start playing poker for the first time in tournaments in a casino and I have two questions.
What are some mistakes newbies make that I should avoid?
and what is considered a good ROI for tournament players, as I plan on playing more tournaments in the future?

Hi OP, I moved this to the tournament subforum as it didn't belong in the STT forum

I would suggest to look at stickies in the tournament forums and use the search function to look for some threads with information on live tournament poker.

I don't really play any live, so can't comment too much, but something to take a careful look at is the structure and rake % as many smaller stake live tournaments are raked quite highly and have very fast moving structures, making it hard to have a huge edge/ROI even if the field is really really soft

thanks a lot. i dont know what a tournament subforum is but i'll look around. and what may i ask is a sticky?
again, first time on site, so im trying to find my way around.

Hi, I'm new to poker and plan on playing tournaments frequently at a brick and mortar casino.
Does anyone know how I determine a good structure for a tournament, and how much is a good rake percentage, and how would I know how much of a rake is being taken?
Also, I read that between 5-20% is a good ROI for live tournament players. If this is true, how can you make money like that? To me, it seems very low.
thanks for your comments.

Good structure? Avoid casinos with small buyins then as they don't have good structures. They want you off out the tournament quickly and onto the wheel. A casino makes no money off you once you've paid $10 rake and are sat grinding a tournament for 6 hours.

Stickies are the threads which are "stuck" to the top of each subforum by the moderators, and they don't move down even if nobody is posting in them.

They are sometimes locked threads, so that only mods can post in them, and they usually contain FAQs, and basic or beginners advice, and tend to be a good place for newcomers to start.

Depending on where you are in the world, for advice on good tourneys in your casino/area you might also find some useful information in the venues and regional threads subforums in Brick and Mortar.

jdawg already nailed the advice on rake and structures in low stakes live tourneys.

GL!