Burrow Charge - Probably the funnest. Mastering this is about getting your Burrow Charge in the right place at the right time. Sometimes it's about initiating, while others is about using after you get behind enemy, or have to use to escape a bad situation. It's Anu'barak's best ability. It uses Burning Rage to add extra damage to those trying to fight you and lets you wave clear pretty quickly. Use this build to perfect your burrow timing.

Harden Carapace - A most simple tool. Just spam it before as many abilities hit you as possible. Can be used for the creation of scarabs as well. Scarabs are useful for blocking shots, scouting, dealing extra siege damage and even finishing weakened enemies on occasion. Use this build to practice timing your shield for other builds.

Basic Attack - This is the trickier one as it is a combo that relies on using Impale with basic attacks. If you do well with Burrow Charge then you can get into position to Impale and then Auto Attack. If you practiced with Harden Carapace build then you should be able to defend yourself better to reduce fatal retaliation.

I personally prefer the Burrow Charge build, but the Basic Attack is more competitive and the Harden Carapace is simplest to use. Have fun!