First, you should immerse yourself in each major topic when you do study. For example, you might take some time away between studying IPSec VPNs and SSL VPNs, but when studying any of it, take the time to read and practice all the exam material in a concentrated time period. The VPN exam has several large topic areas (IPSec VPNs, Clientless SSL VPNs, AnyConnect VPNs, and High Availability) that fit this strategy well. As usual, there is time pressure on achieving a certain level of certification; a wrong approach on studying will eventually haunt you later as more and more gaps in knowledge start accumulating.
Bear in mind that it is not enough to understand the information; you also need to easily remember both rarely-used technologies and advanced, cumbersome ones. For this there is no common approach; you need to make your own algorithm to correlate topics, and make a matrix inside of your brain.
Practice. Buy gear, use emulators, use simulators, rent or borrow gear, but plan to practice the configurations and spend time understanding the show commands. Use debug commands as much as possible to better understand what goes on during a functional configuration. Break it, use debug commands again, and observe if outputs are friendly enough to give you hints on where any errors might be, so that you can understand and troubleshoot the process.
Learn each topic deeply. CCNA and CCNA Security cover a much broader set of topics than does any professional level exam like the VPN one, which goes much deeper but into a certain area. To learn the topics to the required depth, read your primary study sources, review the material, and practice every aspect of it. It's also helpful to use multiple study sources when possible, and practice the commands while immersing yourself in a topic. Also use certified forums and blogs, which often provide good explanations of how stuff works and where you can ask experts about your issues.