Hi jmnelson,
For you GMAT preparation you have chosen a good book, so don't worry as you can strike a good score without the need of tutor. What you will need to do is to keep practicing with books like Manhattan, official GMAT and Kaplan. Apart from this take practice GMAT tests to see how you are doing and where do you stand. We recommend you to keep taking practice tests to enhance your performance. It will help you in identifying your weak areas and you can focus on them accordingly.
You should try this combination to provide yourself flexibility. It could be combination of-
1- Books like- The Official Guide for GMAT Review, The Official Guide for GMAT Verbal Review, The Official Guide for GMAT Quantitative Review etc could be used.
2-Online Study Guide: Websites like Knewton, Grockit etc provide you with practise questions online.
3-Smart phone applications- Kaplan, Veritas etc offer applications to prepare for GMAT on your smart phone
What else can we help you with?