Where to Go from Here
Evaluate where you are in your voice studies. If you don’t work with Cisco’s Unified Communications products in your day-to-day job, you might consider going down the CCNA Voice and CCNP Voice certification tracks first.
Supplement you real-world experience and certification track studies with any of the previously listed resources that might help fill in the gaps for you.
If your budget permits, you might consider taking a CCIE Voice Written boot camp.
Also, organization in your studies is key to your success. Since the CCIE Voice Written exam covers such a breadth of topics, you should go through the exam blueprint, and make a list of all topics on which you need extra study. Then, take that list and identify how you’re going to study that topic (for example, buy a book or read documentation on Cisco’s website). Finally, an approach that I’ve personally found to be very effective: write down on a calendar which days you’re going to be studying specific topics. This level of organization helps ensure no topic goes overlooked.