Heroic is quite easy. For first time, it's better to make sure no two or more players go in the same time so you won't waste damage. Call out is important. We practiced the call out for a few times in tier 6.
You need one guy to solo phase 1and if he can extend the damage to phase 2. Then ask your members to send in one squad each first one at a time, call out always. Reserve some strong players for phase 4 as it is brutal for first timers.
Some would say that you need to be able to do tier 6 in one refresh but we didn't. You just need a few strong players with teebo and tmr toons and don't waste damage by calling out per member. Potency of 70% is needed for phases 2-3. In phase 4, teebo need at least 80% to work so it's better to reserve some strong hitting players for phase 4.
In short, someone to solo phase 1. Call outs. Reserve a few strong hitting players for phase 4.