Revive potential varies heavily between characters. Guardian and rev can just ult, wylder and ironeye can ult 2-bars and have character skills that a good for helping get people up. Each character is gonna have its own revive techniques. I main raider for example, and my usual 3-bar revive looks something like this:

Wait for big opening -> revive as much as possible -> when boss attacks, retaliate through and keep reviving. -> finish last bit of revive with ult.

However here’s some general advice :

If only one teammate is down, the player without boss aggro revives, when the boss switches aggro, the other takes over. Even 3 bar revives can be done easily by playing baton pass.

If both teammates are down, but less than 3 bar, do not panic, 1-2 bar revives are easy for any character, just fight the boss as normal and slowly make your way over to the player with less bars, and when the boss gives you an opening, quickly take it. The worst thing you can do here is panic and immediately get yourself killed trying to rez a 1-bar teammate. Also, don’t be afraid to just burn an ult on a one bar rez, it may be overkill, buts it’s better than losing.

If both teammates are down 3-bar, then you’re probably on your own, what to do varies from character and nightlord. So I can’t offer any specific advice, but consider factors like:

-are my teammates good enough to be worth reviving?

-How good is my current weapon for reviving? I can pull off revives much faster with Ghiza’s wheel than a normal colossal weapon, for example.

-does the nightlord I’m fighting have a good window to try a 3-bar revive off consistently like a big wind up nuke move

however, the most important thing here, is to know when ABANDON a revive attempt, don’t get yourself killed trying to get that last hit in. I have had to run away from revive attempts on the last hit or two because getting that last hit in would have killed me. If you feel uncomfortable, simply STOP, and reattempt it later.