There's no simple answer to this, but you probably should be playing more than you are. You have to consider the situation, the cards, and the price you are getting. Folding isn't necessarily “saving money” – it may be passing on a profitable investment/wager. I think a good rule of thumb is to complete anything suited/connected. In pots with 4+ opponents, hands like K5o are pretty much worthless, but in a three-way pot, there's a far better chance of winning if you make a pair, and I'll often complete with them especially if there are antes.