I am in grad school right now - even at my advanced age! It's a research Ph.D, so I don't have to attend classes, however, I chose to do so, so that I could find out more about what I needed to do to get my Ph.D. I treated it just exactly like the work environment I had retired from - as if I were being paid to do a job. Before starting, i read a number of books on how to get a Ph.D but I don't think they were much use because it wasn't until I started that I found out what it was I didn't know. The classes were very useful. The books I found of most use were "A students' guide to methodology" by Peter Clough and Cathy Nutbrown and Critical Reading and Writing for Postgraduates by Wallace and Wray. It was also very useful to read Peter Elbow's book on writing and Rowena Murray's book on "how to write a thesis". They both talk about just getting down and WRITING. Don't wait til you have something to say - just write. 100 words, 5 minutes, write anything. Murray's book has useful prompts for writing.
Most of all READ. Read everything you can online, hardback, softback etc, about the subject you are going to be studying. Remember, you have to find something original - find the gap that no one else has written about. How will you find that gap unless you know a lot about the area?