Since the Network+ exam covers a broad spectrum of networking topics on its blueprint, you should consider a CompTIA Approved book that targets the N10-007 exam. CompTIA's approval ensures that the book covers ALL topics on their exam blueprint.
Alternately, if you have a training budget, you might prefer to take a class, where you can interact with your instructor and fellow students, ask questions, and get hands-on experience with the equipment you are studying.
Note that hands-on experience can also assist you in preparing for the exam. You can even use a couple of older PCs (running Microsoft Windows® or the Linux distribution of your choice), an older (less expensive) Ethernet switch, and a home wireless router to build a practice network topology. Practicing Windows® and Linux commands and becoming comfortable configuring network options (for example, configuring a static IP address, default gateway, and DNS), and troubleshooting any issues you encounter as you build and work with your home lab. A small wireless router would also allow you to practice with the frequencies, security, 802.11 protocols, and other settings. This practice can help you dramatically in your preparation for the exam.
You should also note that many simulation options exist for you today in the area of Network+. Low-priced simulators allow practice with hosts, routers, switches, and even the wireless equipment you are expected to know.
To prepare for the subnetting questions you might face, you can make up your own practice questions, for example, "The company in the topology below wants to use the address space of 10.1.2.0/24 for their 3 sites."
"What subnet mask could be used to create 4 new subnets?", or "What would the mask be to support 16 hosts?" Then, you could use a free subnet calculator from the Internet to check your answers. Remember, of course, that such a calculator would not be available in the actual exam.