First offer you get is probably around 10% less than they will go if pressed. But you need to be prepared to walk away if they refuse to budge.
As far as needing/deserving a raise, that means nothing to the company. Look at it from their perspective, not yours:
Are you doing the work at your current salary?
Do they have a reason to believe you are prepared to leave?
Can you be replaced if you leave?
You should ask for as much as possible in interviews and have a very firm low number. if they go below it, then it's not the right position for you.
One bit of advice would be to never ever give your salary history or tell them your salary requirement. No matter how much they ask, make them offer first. If they don't, walk away.
