Although the class has largely fallen out of favor, seeing the resurgence of player population due to COVID-19 lockdown, I might as well write a simple guide for new or coming back players into it, which is still my all time favorite.
Herald is all about energy management due to the unique energy system of the revenant class. For beginners the task could be difficult at first, so here is a quick guide on how to manage your energy consumption effectively and efficiently by identifying the situation you are in.
For the build, please refer to the following link to metabattle.com.
Camp in Glint and maintain all three utility Facet skills to buff allies with Fury, Swiftness and Might.
Drop Facet of Elements with Elemental Blast. (Or alternatively, if your group is skipping this phase and portal/stealth bombing, keep it and skip to #3 below.)
Range with Hammer. If its a staredown at a chokepoint, preemptively disarm enemy Marks and Traps with Phase Smash (#3). Do not bother with Coalescence of Ruin (#2) unless collective range pressure is called for, since the result is usually inconclusive during this stage; stay in combat to slowly ramp up your energy over 50% and Might stacks.
If enemy projectile pressure is present, apply Field of the Mists (#4).
At 900 range, Drop the Hammer (#5) on targets within allied Sand Shades radius while closing in. Cast Coalescence of Ruin on the said targets.
At 500 range, activate Facet of Chaos (#0) to grant protection to allies, and then immediately cast Chaotic Release (#0) at the enemies within ally Wind of Disenchantment.
At melee range, cast Burst of Strength for damage buff and then again Elemental Blast and other big damage skills on the controlled or downed enemies. Or alternatively, save your burst rotation until a heavy damage bomb is called for.
Also, preemptively activate Facet of Light (#6) before melee so you can immediately access Infuse Light (#6). Don't worry about the effectiveness of Regeneration you provide, as the same boon from other, better sources would come into effect in advance of yours.
Cast Gaze of Darkness only when you must break out of stun. Drop the Hammer (#5) at your feet if enemies are on your tail. Though Phase Smash (#3) helps you evade incoming attacks, you should avoid casting it at this stage unless your group is stationary, so you do not get caught lagging out of place behind your group after the returning animation.
Switch to Jalis if:
A. Gaze of Darkness is on cooldown and you need Rite of the Great Dwarf (#0) to break stun.
B. Infuse Light (#6) is on cooldown and you need Soothing Stone (#6) to heal or counter heavy condition pressure.
C. Your group needs additional source of Stability. In this case use True Nature (double-tapping F1) first as it does not cost you any energy. Only then use Inspiring Reinforcement when you must, or when your group is moving through a hot chokepoint or out of a hot spot.
D. Your group is under pressure and requires damage reduction from Rite of the Great Dwarf (#0).
E. You run out of energy with Glint and the Facet/Consume skills are all on cooldown. In that case there is no point camping in the same stance anymore.
If your group is constantly under heavy pressure and not handling well, you might have to save all the energy for Rite of the Great Dwarf spam.
If Draconic Echo is selected for the Grandmaster trait in the Herald Specialization, which I personally would also advise for, try to Consume all activated Facets before switching to Jalis.
Switch to Staff if:
A. You need healing (#2 & #5), blocking (#3), group condition cleansing (#4), and/or evasion (#5 & Sigil of Energy).
B. You need to move through or out of a hot chokepoint with Surge of the Mist (#5).
Avoid using Vengeful Hammers or Forced Engagement unless it is a certain wipe for the enemy group and you want to maximize your tagging or to single out an enemy already low on health trying to break away.
Switch back to Glint as long as your group is no longer pressured. Switch back to Hammer when your group is again on offense. Repeat from Stage 2 or 3.
Now, if you are out of combat during this stage and really want to push it to the limit, switch to Renegade to cast Orders from Above (F3, Alacrity), and then immediately switch back to Herald before the next engagement. The effect would last even after you switched out of the Renegade specialization. Use build templates and hotkeys to speed up the process. Make sure you select the associated Grandmaster trait (Righteous Rebel, the bottom one) so the boon is shared with 10 allies.