I've found the main stumbling block to be humidity. If the humidity in the growing area is not high (I don't know exactly how high it needs to be, but 50-60% is not enough) then you tend to get a lot of brown tips and very little growth UNLESS you have a dense clump - then you still get lots of brown tips but it will grow.
Knowing this, it's actually pretty easy to get started. You can take a simple plastic container like a plastic take-out tray, add your starter sphagnum, get it nice and wet, and seal it up. Put it near your growlights (but no sunlight, you don't want to roast it!) and let it grow.
For outdoor growing, you can fill up a regular pot halfway with soil with sphagnum on top, then place it in one of your water trays. Being recessed in the pot will help elevate the humidity. If you want to grow in a larger container, you'll likely need to keep the water level very high or the sphagnum very densely-packed.