EFFICIENCY
To make the big Eve Isk  with a POS, you have to keep your operation running as efficiently as possible. This means lowering fuel costs and initial investment, maximising sale prices and minimising time and effort spent. Luckily, there are a lot of tricks to keeping your operation efficient, both in profit and time.

The single biggest key to efficient moon mining operations has to be using Caldari large towers. There is no doubt about this one - Caldari towers are simply all-round better for industry due to their massive CPU load. This is because all industrial modules, such as reactors, refineries, silos, etc use a large amount of CPU. The Caldari large tower, specifically, has enough CPU that it can do something no other tower can - successfully run both a simple and a complex reaction on the same tower. In fact, a medium Caldari POS could feasibly run a complex reaction using coupling arrays to feed it and collect materials, though this would need to be attended to every 15 hours.

Setting up near a station or outpost will dramatically cut down hauling, as you can hire a freighter to go from there to Jita and back for fuel and selling product. In addition, a common operations strategy is to simply empty the silos daily into a corporate hangar array, then haul it all to a station once a week. This drastically minimises hauling. Since all of my setups use 100% of the available CPU, not leaving any room for a corporate hangar array, I keep one anchored but offline. You can take items out of it when it is offline but you can only put items into it when it's online. Therefore, the only times when I need it online are when I am emptying the silos into it, in which case the silo is offline and not using CPU. In that way, I technically have enough CPU spare to use the corporate hangar array.

There are also a good number of ways to cut your fuel bills and thus increase profit. If you set up your POS in 0.0, say as part of an alliance, you can claim a sovereignty bonus. A POS in a system in which your alliance has sovereignty benefits from a 25% reduction in fuel usage. That translates directly to increased profit and reduced fuel hauling. However, the risk of hauling in and out of 0.0 may make it no longer worthwhile. Thus, be sure to consider the pros and cons carefully.