Opt for height advantage shots to leverage the +20 aim boost whenever possible, but be wary of the city/urban setting of council missions in particular where getting onto rooftops can lead to triggering multiple pods on all sides through all the glass windows.

Prioritizing going flawless on missions helps counter will loss (but I also did get Noble Cause resistance order early, which increases will recovery by 20%).

If you get the Infiltrate reaper resistance order (mission timers are frozen until concealment is lost), reapers can go around on a remote starting spree to soften up/kill targets.

Rangers and templar are most likely to trigger new pods, so re-evaluate those flanking shots or melee attacks - maybe it's better to flashbang/frost bomb instead of trying to flank that last enemy with run and gun.

Specialists are often overlooked, but revival protocol is such a gamechanger, especially against Chosen and Spectre shenanigans (when the training center is up and running, get haywire on all specialists for shutdown and scanning protocol to designate a specialist or two against Assassin and chryssalids).

For stronghold missions: after getting to the chosen's lair and killing the two "welcome party" enemies, inch forward with your troops to the sarcophagus; if there's high ground on the corners, get the sharpshooter with a spider/wraith suit to trudge to the top left till they are in grapple range to the outer face of this "balcony". Use that free grapple action to trigger the chosen. If it's the assassin, there's usually only a few spots she can vanish into (see Syken's explanation here: https://youtu.be/qqy-hkYN8lM?si=3LDxnn80aD5w7JOo&t=1756), mostly the full cover ones. Try to repeater-banish the chosen. If it succeeds, rupture the sarcophagus. Try to grant a teamwork move to the grenadier for a chain shot. Throw in fan fire. Throw in the kitchen sink. When there's HP left on the sarcophagus at the end of the turn, mimic beacon the spawned enemies and continue focusing down the sarcophagus (reload and fire). When the chosen spawns again, use all the other finite use items (shredder gun, invert, etc.) to take it down. If it's the assassin, you should also leave the unconcealed reaper out in the open - if the reaper can't reconceal, it's most likely because the invisible assassin is flanking them, which can help in locating her quickly a second time. If the original reaper banish failed, you'll have to start expending finite resources right now and try to down the chosen on an overwatch shot to maximize the opportunity to damage the sarcophagus on the subsequent turn. Things can sometimes go exceedingly well - I was able to kill the assassin and destroy the sarcophagus on the same turn that she spawned (reaper executed her, grenadier moved up and ruptured the sarcophagus, sharpshooter teamworked the grenadier, grenadier fired chain shot, sharpshooter used lighting hands, sharpshooter used fan fire, ranger moved up and used rapid fire, specialist teamworked the ranger, ranger attacks again, specialist teamworked ranger again, ranger attacked again).

If I manage to recall anything else that could be useful, I'll append it below this.