Not only did it take my group forever to finish off this particular giant lair (basically, my fault), this video also runs a bit long... So if you just want the meat of my advice, watch the beginning and the end using the index below.
Addendum: One thing that I don't think I stressed enough in the video, is that I didn't create enough of a sense of urgency. As an example, the party didn't know Guh had prisoners that were on the menu. Even when the thief scouted, he did not specifically scout the prison area. I should have created a scene for him to witness with the prisoners suffering at the hands of the bugbears or similar to emphasize that time was a critical factor in their assault on the lair.
01:45 Considering the challenges in running a large lair with a multitude of opponents
2:00 Will it be a cakewalk or TPK?
4:20 How will the lair react once combat breaks out? Where will the creatures move?
6:40 When the PCs do commit, how to the monsters react based on their intelligence and allgiences?
8:40 How does one present clues and options to the players without telling them what to do?
9:00 When you group meets infrequently, how do you optimize sessions and keep momentum to get through a large lair like Grudd Haug?
10:00 - 35:00 My group's hit and run tactics on Grudd Haug
38:48 Send opponents in waves to amp up the combat pressure.
46:45 Give scouting hints.
47:10 Don't save them if they get over their heads, but consider non-TPK options if it happens.
50:00 Don't hold back intel. Better to overshare clues to keep them party moving than to give them too little.
52:00 For giant lairs, chop it up into larger combats, instead of lots of small combats with few opponents. YMMV.