newbies mistakes in learning poker

You play too many hands
You ignore the size of the pot (including chasing with bad pot odds)
You call 2+ small bets cold pre-flop with unpaired offsuit hands (AQo, AJo, QJo, KTo, etc.)
You don't raise AKo,JJ,TT
You don't 3-bet/cap AA,KK,QQ,AK
You fold pretty good hands for 1 bet in big pots
You open the pot for a limp outside of UTG/UTG+1 at a full table.
You think you can push out a flush draw
You play unsuited cards with one big card and a little one
You play suited crap out of position and for more than one bet outside of your blinds
You jam your draws without enough pot equity (callers) and/or with very little fold equity destroying your implied odds in the process.
You raise the flop "for a free card" too often and then proceed to semi-bluff the turn anyway.
You play your blinds too much when facing a raise (particularly heads-up)
You think playing over-cards is your biggest leak
You don't bet the river often enough
You go all-in
You over-value deception against poor players
You under-estimate how much of your profit comes from AA,KK,AK
You under-estimate how much of your profit comes from players that suck worse than you and fail to seek them out.
You under-estimate the impact and diverse forms of luck over the short term.
You under-estimate what long term is. 10,000 hands isn't long-term.
You expect to beat the rake for a healthy rate in any live game smaller than 4/8.

There, I've saved you the $30-$50 it costs to buy half of the Poker Books on the market today