U should use spells just for spawn Scarabs at the very beginning. If U dive under towers, the Scarabs will take the first shots.
Burrow Charge in, hit them whith Harden Carapace (from lvl 13), and stun the focus target with Impale.
Anub is much more effective when u can warn the team: NOW I'll go in!
Burrow Charge is also useful for escaping, this is more effective if you go through walls.
Use Cocoon soon as it ready to get rid of the hero which causing the most trouble for your party. The healer is usually a good chioce, expect it is on focus already. NEVER Cocoon the focus!
With Dampen Magic, U can absorb a high amount of dmg, so use it wisely.