The most important thing to remember when you fight in the spire is to make certain you have as many 5-day military buildings as possible. Those are the ones you craft in the magic academy. It's simply too difficult to fight without them. If you have a Fire Phoenix, make sure you feed it. If you don't have one, try to get one ... they are sometimes offered in the magic academy, along with artifacts. Get as many artifacts for it as you possibly can.
The five-day buildings are the easiest way for people who aren't the best fighters to make their way to the top of the spire. Collect a bunch of them, and until you are strong enough to do it weekly, just go for a "push" once a month or once every few weeks. Save as many 5 days as you possibly can, particularly the unleashed unit upgrade, the enlightened light range, and the mage mulipliers. The newer ones, like the 5 days to boost melees, heavy range, and light melee, are useful but not as important.
I usually put out at least two of each. If you have a dwarven armorer, put out that too. A lot of people will tell you that is overkill, but trust me, if you aren't much of a fighter or only do autofight, it is not overkill. I don't even think three of each are overkill depending upon your circumstance.