Build the highest number of hatcheries that you can at one time, and spend your gold to upgrade them as high as possible. Every battle that you fight, whether it be a campaign or against another player, is a numbers game as much as anything, and more hatcheries will allow you to train more minions at one time, and have a higher maximum number of minions. The more that you upgrade your dungeon heart, the higher maximum number of hatcheries that you will be able to build.
Build the training room as soon as you unlock it as well. The training room will allow you to upgrade each individual one of your troops. This means that if you have a favorite, you can make your favorite even stronger. So theoretically, you can send in a massive number of skeletons when you have multiple high-level hatcheries, train the skeletons using the training room, and defeat almost anybody that you want using the most basic minion in the whole game.
Another trick is that any time you are attacking someone else’s dungeon, whenever you destroy any one of their structures, you will then be able to use that structure as a spawn point. This adds to the strategy involved in that you can send in the minimum number of troops necessary to destroy a few structures, then send in more minions later on using the spawn points to instantly get that much closer to the dungeon heart and the resource storage facilities.
The guard post is another one of the most important buildings that you can have. Purchasing a guard post will allow you to unlock in mortals. If you have ever played Castle Clash, and are thus familiar with the “heroes” in the game, but in mortals in the Dungeon Keeper are similar concept. They are more powerful minions who will live even after any battle that you use them in, and the more levels that they fight and, more powerful they will become. They can save you serious gold on training troops.
Remember that you can move any one of your structures around besides the Goldmine, the stone quarry, or the dungeon heart. Do this by tapping and holding any structure. It is highly recommended to move your treasury and your stone storage. Almost nobody moves them, so anybody who attacks you will be thrown completely off guard. This also allows you to move them closer to the dungeon heart so that other players will have to work harder to be able to get to them, and you will be able to place more traps and defense rooms in between the spawn points and the storage points.