This idiom means to negotiate in a forceful way or demand the best terms for yourself when making an arrangement or deal, especially with regards to the price of something. Somebody who 'drives a hard bargain' can be difficult to deal with, but the term is usually used in a positive sense. It takes skill to make an arrangement as favourable to yourself as possible without ruining the chances of reaching an agreement, and shows that the person in question is somebody who knows what they want and is willing to work or fight hard to get it. While this expression can be used in certain social contexts, it is more common in a professional one. Phrases with a similar meaning include 'stand your ground,' and 'beat somebody down.'