tip 1:you don't wanna crowd your dungeon with bosses,stick to about 4 bosses and one more powerful end boss
tip 2:alot of quests usually involve dungeons,so you might wanna make a few of those quests
tip 3:yes,you can have none hostile NPCs in dungeons
tip 4:don't make your dungeon a straight rectangle or something,make it completely random and not too easy to navigate
tip 5:dungeons should have traps,bonus items,puzzles ETC,otherwise it'll be just like any other map
tip 6:make sure the enemies are harder than enemies on regular maps,especially make the bosses hard
tip 7:try to make your dungeon have a few modes to choose from easy,normal,hard ETC
tip 8:please don't rush,there's nothing worse than an uncompleted dungeon
tip 9:make obstacles other than enemies,oh yeh,i already mentioned traps