Here is what I do step by step:
1. Figure out where to put it
2. Put it where I figured out
3. Build the lip
4. I usually let it sit for a couple hours/overnight
5. I use either a metal rake, or just a regular garden rake to "groom" what I need to. This helps to get rid of some excess snow and fill in areas that have little snow on them.
If you have a really powdery fine snow, use much, much more then you need. I go by at least three times what I'd normally need, and pack that, and if it's larger than it needs to be, pack some more, or just shave off what I need to.
Water works well to help a lip hold its shape if it's below freezing, and salt if it's above. Once you make a couple different setups and lips, you can just start to eyeball what you need. But also sidestep the landing/trail that you'll be using. This will obviously help to pack it down, and if it's a fluffy powder, then packing it down will improve speed.
Hope this helps.
