I can't recommend a book but would advise you to look at the various government employment websites that are in the area where you want to work.
I'll give a couple of examples from here below. If you are not a MS guru, you need to take some classes or self-study online. Almost all government employers are big MS Office/Outlook users, and recently have started getting into Sharepoint. I'm a hiring manager at a public agency myself and we require that people be at least intermediate users since every position is expected to use MS products on a daily basis in addition to other more specialized software depending on the job. We will ask people to rate themselves 1-10 on various MS products and depending on the position anything below 5-7 could be cause for rejection. We also use follow-up questions to try and catch those that might overstate their ability.
AWC JobNet - Search Jobs
https://apply.govjobstoday.com/