Sadly, not everything is negotiable. As Waixingren said, Uni salaries are set and they won't negotiate on that. You might be lucky and be able to negotiate on hours etc, but I doubt it. The ad will clearly state what is expected of you and what you'll be paid. If that doesn't suit you, find something else that does. Experience is the key here and the more of that you have, the easier it'll be to negotiate. Just be careful, look around and take your time!
Again, good luck!
