Lex deals too much damage to fight on your own. If you're under attack from him, use Shadow Travel and move to a safer location, then regroup with your team.

Ruckus is vulnerable when he uses his ult. Remain out of his focus and shoot him down.

Treacherous Ground shuts down Maeve's mobility quite handily if you can catch her with it, but be wary of nearby terrain. A smart Maeve can use some bits of map geometry to get above the effect of Warder's Field and become free from the cripple.

When Inara is using the Treacherous Ground talent, keep your distance from her. If you get caught in her Warder's Field then you'll have no good way to get out.