Great guide! A few I would add:

DO be careful with your knockback skills. DO NOT knock a tough enemy back into another group of enemies. Many team wipes in Numa levels are caused by this. Give somebody the chance to lead it back a little where you can knock it sideways, then you can use the knockback.

DO NOT try to lead the group as an Operative, UNLESS you are willing to keep yourself alive with stims. Otherwise you just waste a lot of the engineer's power when he/she has to revive you constantly.

DO let a teamate die when they are constantly doing things wrong. Better to revive just one than wipe everyone just to save a loose cannon that will die anyway. They will either get the hint, or leave.

DO stay together, even when you think the group is going the wrong way. Some groups skip parts of maps in order to get to the boss more quickly.

DO NOT try to mesmerize a mini-boss. Let someone with higher armor engage that enemy while you and the others get rid of the weaker enemies. Engineers have a skill called Pain that works very well on tough enemies. Use that instead of the mesmerize.