Working the bid/ask for options is part art and part science. While there isn't any apparent liquidity in most options, behind the scenes it's quite a different story. There are hundreds of institutions out there running computer models trying to take advantage of mispriced options. The use various models, such as Black Scholes, GARCH, or internal proprietary models.
So, let's take a real world example. Dell computers. Jan 12.50 call. Right now it's traded 57 contracts. That's not a whole lot considering its one of the biggest companies in the world, right? Currently there are 272 contracts bid at 2.15 and 15 ask at 2.23. Not a lot there, either. So, we can learn one thing from this. Someone on either side is willing to take a theoretically incorrect price for Dell. There's some small player (i.e. you or I!) out there willing to let 15 contracts go at 2.23. I know from experience that if this player wasn't in the way, then we would see maybe 2,000 bid vs 1,900 ask. Why? Because those are the arbs working behind the scenes. That's the tricky thing about trading options: because of the constant hum of computers searching for arbitrage opportunities, you're NEVER going to get the theoretically correct price. In other words, in order to actually buy or sell you're going to have to pay up or accept less than the correct value. Believe me, you're not going to beat a thousand of the world's most sophisticated PhDs with their fancy computers.
NEVER EVER EVER EVER put in a market order for options. Why? Well, because as explained above, if you accept the bid or ask then you're letting someone cash in on an arbitrage opportunity at your expense. And given the wide spread it's going to cost you big time. So, what you have to do is thread the needle. I mean, all us traders here are not arbitrageurs. We're trading based on where we think the direction of the stock is going. So, with Dell, if I wanted to buy now then I may put in a bid at 2.18 and see what happens. Once I do that it goes up on the Level II. Someone can see that and choose to hit it. I don't mind paying up say .10 more than the current bid because I know if the stock goes up 3% tomorrow then I'm looking at a 20% profit.