There is only one book to send to someone serving a sentence like that. It is the California State Prisoners' Handbook available at http://www.prisonlaw.com/ located inside San Quentin. It covers every aspect of prison life with precise instructions about what to do when problems arise. It also has a very useful section on habeas writs and how to do them. This is the only resource that directs its attention on prison life. You can't buy it and send it to him yourself but you can paay for it and the Prison Law Office will ship it to him. It is invaluable.
There have to be some good books in the law library at the prison. CEB (Continuing Education of the Bar) puts out a book called "Writs and Appeals," that is a great source. It's two volumes right now. There is also the reference book we all use in criminal law, also put out by CEB named "Criminal Law and Procedure." These are good starting points. He's going to have to focus on his particular issues, that means he's going to have to get into the caselaw itself. Caselaw changes daily as the courts decide new cases.
If his case is on appeal he will/should have an attorney helping him. The law is quite complicated and it can be a minefield for a lay person trying to figure it out. I hope he get the help he needs and if there were mistakes made in his case, that he finds relief in the courts.