This is what i use to farm focus in ESO while reaching 8 waves for a chance at a good reward.
The ideal squad for this is [Mirage] [Volt] [Rhino] and [Trinity]. [Trinity] is just there to give energy and [Rhino] to spam his 3 for the damage buff.
[Volt] is nearly mandatory if you want to farm efficiently : with 4 corrosive projections, his 4 will kill the first wave of ennemies at the start of a round instantly allowing you to start using your 2 and build it up very fast (the more loot drops, the more explosives you have on the ground). Without [Volt], it's way too slow to be efficient. However without [Mirage], the focus per wave is way lower.
If you're going to play in public without building an optimized squad, you should stick to [Volt] if you see 4 CP in your squad, otherwise [Saryn] is the safest bet to go 8 waves no matter you squad but you may not [Reach] focus cap because her kps is so much lower.
Your 2 will transform any loot into a damage dealing aura, only use it AFTER a wave of ennemy died, using it at the beginning of a round before [Volt] has had time to kill anything will just waste your energy. After that, spam it whenever you see a batch of ennemies dying, it's a snowballing process up to the point where everything litteraly gets spawnkilled (if you have the right squad).