I'm an ugly fly caster. I learned nearly 50 years ago from anglers who were highly skilled at finding fish and aggressive waders. So I while I can single and double haul and present flies, poppers and such to enough fish to catch all I want, I'm hardly worth watching on the stream, unless, of course, you like to watch fat old men stumble about.However, when I see someone like Stu Apte or Lefty Kreh fling flies on saltwater, or watch Dave Engerbrentsen and some of our local Clearwater River steelhead fly specialists cast far and fine, or for that matter, watch a properly shirted and tied Brit "present" a fly on a chalk stream, I'll set my rod down and watch. So it's "Do as I say, not as I do."
First, and this is from my experience as both a tennis and x-c instructor, get help early! If you can afford it go to an Orvis or other casting weekend. If you can't afford that, check at the local fly shop for lessons. Some offer free casting lessons if you buy gear. All should! If that fails check out the local flycasting club. Most clubs offer casting help and a pointer to decent local waters. Finally, if all else fails check out the lovely videos in 3M's Mastery Series and get a buddy to help. If you don't have a buddy, set a mirror so you can see yourself.
Just remember: the narrower the arc between the forward stroke and backward stroke of the cast, the tighter the loop. Then too, if you do this in the yard with a little bit of yarn on your tipped end, you might want to reverse the line before you fish. Grass does nibble at line coatings. It's also wise to start casting at something, rather than at random. Don't, unless you're a steel header, worry about length. Aggressive wading can make up for distance deficiencies.
Once you learn the basic cast, try a roll or a loop by turning your wrist. Videos and books have specifics and you don't have to do it exactly like the pros to catch fish. You should, however, start with some video or ad persona help. It's much easier to reinforce good habits than kill bad ones!