Know how much the job is actually worth, and be prepared to walk away from the opportunity if they don't offer it. If they're offering you 10% below the market rate, then ask for 15-20% more (55K-57.5K) and don't settle for less than the market rate of about 53K. Don't ask for silly money unless you're prepared to walk away from the opportunity.The most important thing is to make an effective argument - give them data to show what the market rate for this kind of position is.