You want to make sure the fly line fully extends during your back cast before starting your forward cast. You should smoothly accelerate your rod hand to a hard stop to get the fly line to extend behind you in a straight line. You should position yourself so you can watch your forward cast and back cast. Staggering your feet should help this. Watching your back cast is a good habit to get into early to help with timing and accuracy (I saw your were doing this in one of your videos).
Gink and Gasoline has a great article on why you should always watch your back cast.
http://www.ginkandgasoline.com/fly-fishing-tips-technique/why-all-fly-anglers-should-be-watching-their-back-cast/
You also want to make sure you are not stopping your rod hand too far back at the end of your back cast. Your forward and back casts should be making a “V” or a slice of pie. For short casts that do not require a lot of line, your slice of pie should be small. As you let out more fly line for a longer cast, your slice of pie will get larger. And just like in real life, your slice of pie should be smaller than you want. If you don’t let your fly line extend or let your rod hand drift too far back at the end of your back cast, then the fly line will arc during your forward cast. This is difficult to correct and will usually require you to restart your casting from the beginning.
Also, you want to make sure your casts are in straight line. If you divide your body vertically in half, your fly line should not cross the middle line. Think about the motion your arm makes when driving a nail with a hammer – this is very similar to what you should be doing during your cast. Watching your back cast will also help keep your line straight.
Free casting lessons should help. Feather-Craft in St. Louis also offers free lessons.
Also, here are all the Orvis casting videos:
http://www.youtube.com/playlist?list=PLjXHFe6IPFJx-8aREYYfUA1TKrTEMxBnS
I think you are in my area. I’m not a casting instructor, but I’d be willing to watch your casting and give you some advice. Send me a message if you are interested.