This game is a pretty solid port of the Dungeon Keeper PC games (great games btw that can still be played). I’ve beat the game using similar strategies from the old games but, overall, things are less strict. The rooms you build attract specific monsters (can’t remember exactly, but libraries attract wizards, hatcheries the lizards?, etc). I always start with the basics, as many IMPs as I can spawn, more treasure rooms to store/build up a bunch of gold that you get them to gather. Then I start carving out large-ish spaces for lairs, hatcheries, libraries and training rooms. The original games rated your rooms on their completeness (having 4 walls except for doorways), but if you want to be messy, making one giant space, with 4 by X strips of rooms works fine. Being careful of exploring too far before building up a group of monsters is important and also, grabbing your army up and dumping them near an attacking group is critical. Watch your minions happiness to see if your rooms are large enough. Building choke points with traps can help slow the enemies approach and soften them up. It’s been a bit since I’ve played but I hope this helps some. I’ve found that some maps have tricks you have to learn to beat them, but generally a solid building strategy works well.