Hi Maria,
We had a few of these lying round the department when I started. I can whole heartedly recommend "Your Ph.D. companion" (Marshall and Green). Its written with wit, not bogged down in unnescessary detail and easy to dip in and out of. Avoid "How to get a Ph.D." (Pugh) because it's written like a Ph.D. thesis... I found the former to be quite motivational and the latter to be confusing. Worth noting that I'm talking from a science point of view.