I play every now and again in the kind of mates games you are talking about and the following has always stood me in good stead, I am usually in the top 3 out of 6.
Learn the hands and what beats what, even if you are going to pretend to be clueless.
Constantly evaluate what potential hands are possible with what is on the table – beginners often get obsessed with what they are holding.
Conserve your dough – don't be tempted to throw money in unless you are sure what you are doing, most people expect beginners to be clueless so bluffing is dangerous, but this can work for or against you…
There is no harm in folding for cheap and watching how everyone else is playing.
Don't throw good money after bad – fold and conserve the money for a better hand.
Don't get involved in hands with lots of players involved, it is far more complicated, it can get expensive, and you have less chance of predicting the outcome than you have in a one-on-one.
With a bit of self-control, playing your hands on their merit, and with the odd bluff, you should stay in the game long enough to get an idea how everyone is playing.
Most of this advice is only valid for games with mates playing for a decent amount of money and wanting to make an evening of it. I hate playing for too littl money, everyone gets bored and bets like idiots and there is usually a couple of player with a massive chip-lead based on a couple of lucky hands at the start.
Don't throw all your money in and go and watch TV, stick at it for a full game, learn a bit and then decide whether you want to play again.