[Hoskinator]

important things to consider is

what they raise with
do they bluff - are they stealing pots with bluffs when no one hits the flop.
how aggressive are they preflop and postflop
how tight are they - tight players will often fold if they haven't hit the flop, you can use this to steal their blinds and bluff them
Showdowns - does a player always head for a showdown with any pair and don't bluff them if they do.
coldcall - what do they cold call with

without stats you want to get an idea of how many hands they play and what hands they raise with. If they are very loose then you can tell their hand strength from raising.