Dungeon Keeping wouldn't be very rewarding without some Lackeys to push around. Creatures make up your workforce and army. They are your eyes, ears, and hands. Of course, before you can use these creatures to best advantage, it helps to know what your little evil helpers are capable of…
Monster Management 101:

The most important skill for any Dungeon Keeper is learning how to manage your minions. You can amass all the gold and spells imaginable, but none of it will do you any good if your forces are slaughtered due to lack of experience, poor deployment or--Hell forbid--by ridiculous infighting. The real trick is to know your monsters' strengths and weaknesses, and to make sure that you have the right menace for the job.
The biggest mistake novice Dungeon Keepers make is deploying inexperienced monsters. Literally, if there is any monster less than third level outside of your Training rooms, you are either in the last moments of a fight to the death or you are soon going to be on the losing end of one. No minion, from Imp to Dragon, is very effective until at least third level, where some special abilities start to come in. Resist the temptation to throw your troops into battle en masse; the truth is that even a Horned Reaper dies embarrassingly quickly when it's only a fledgling first level.
You should also resist the temptation of prematurely putting monsters to work researching or building traps. While you want your Libraries and Workshops producing as soon as possible, higher-level workers not only do their jobs faster and more efficiently, but they also make much more effective guards for these important rooms. There is nothing worse than a single fifth-level Bile Demon wandering in to massacre your geeky spell research staff of ten first-level Warlocks. And do not forget that a third of your Imps should be in training at any given moment, until your entire construction staff is above the third level.
Unless you are severely strapped for cash or building space, try to build at least one small set of support rooms (Lairs, Treasuries, Hatcheries, Training Areas, and so on) so that you have somewhere to separate some of your more provincial minions who tend to come to work with some awkward prejudices. This racial strife, while not a huge factor in the long run, can make your life as Keeper a living nightmare. The following monsters still have some personal issues to work out--it's best to keep them as separate as possible, namely by moving them to your backup Lair and making sure the odds are highly unlikely that they will bump into each other at all

Bile Demons and Skeletons
Warlocks and vampires
Flies and Spiders
Hell Hounds and Demon Spawns

Creature Feature:
 

1-Imp.
2-Fly.
3-Beetle.
4-Spider.
5-Bile Demon.
6-Demon Spawn.
7-Dragon.
8-Warlock.
9-Troll.
10-Orc.
11-Tentacle.
12-Skeleton.
13-Ghost.
14- Dark Mistress.
15-Vampire.
16-Hell Hound.
17-Horned Reaper.