Any advice before I read Friedrich Nietzsche?

I bought The Will to Power yesterday and I’d like to get some feedback from those who have ever read Nietzsche or have any thoughts on him and his work. How difficult is it to read his books? What should I know before reading his work? Do you recommend doing anything before I read it? The Will to Power seems like a pretty negative book. Is it? Are all of his books full of criticism?

And just a side note: I’m reading this for myself, not for school.