I started fly fishing and tying my own flies back when I was fourteen years old and living at the base of the Rockies. Hard to believe that was 40 years ago, but it was. In my twenties I was asked to give fly casting lessons to beginners at the regional conclave for Federation of Fly Fishers. Me and Lefty Kreh were the casting lesson guys at that conference. Talk about a humbling experience for me as a young man who thought he was a pretty good caster and knew what he was doing. Haha. Anyway, I have taught numerous friends and family members how to cast flies over the years. I concur 100% with the great advice our OFF clan is giving you. There is a lot of fishing experience on the site, and that it is shared so freely is an impressively generous resource to all involved. I agree most with comments that apply to casting accuracy and learning to read the water. As you get the hang of these two skills the rest is easier being a simple matter of learning the nuances through a combination of studying and trial and error. Maybe I missed it, but the one piece I do see missing in comments here is fly casting practice time. When you're actually in the water you'll be dealing with current pulling your line, current pulling on your legs, feet slipping on wet rocks, hooks catching in your clothes, line tangles, trees and grass tangling with your back cast, snags on the river bottom, wind pushing air born line all over the place, and so on. The time to learn to cast is when you are at home on dry ground when most of the variables have less power to interfere with perfecting your casting technique. Watch videos and read about technique and all of that, but put a dinner plate on your lawn and practise casting to it. Don't do it for hours on end, but 20 minutes a day, maybe 3 or 4 days a week before, or after work. Remember the movie A River Runs Through It? The boys were taught to practise casting in their yard to the rhythm of a metronome. That is a real thing and how I learned long before the movie was made. Once you have the basic rhythm and are able to keep your line horizontal in the air in front and in back with just a little fluff tied the end of the leader, then start increasing the distractions. Add a small fly at first, then a larger one, then later start adding a little steel shot weight to it. The lawn is the place to learn to roll cast, bow and arrow cast, side arm, and change casting arms. Practice casting from a kneeling and sitting position to simulate float tube, drift boat and fishing from concealed locations to keep clear low water fish from spooking. Even better is to practise casting on a pond in a park if there is a place to do it easily near work or home. You will find that getting the basics down accelerate your improvement while on the water fishing, and get you over the hump so much faster. It will make the overall experience less frustrating and much more enjoyable. Ultimately, you will be able to walk through current over slippery rocks while false casting and reading the river in front of you in prep to throw to your next fish without stopping. The idea being efficiency, the more time your fly is on productive water the more fish are going to be caught. I think you will find casting practise to be a mind cleansing experience similar to meditation. It can be fun, and it will make a big difference in getting to a place where fly fishing is an immensely fulfilling experience. One filled with peace, lots of fish, and increasing numbers of big fish. Good luck out there!
ideally it is good at 3 to 4 ft, but I watch the levels at Leaburg because of steelhead. I am itching to get in some spring fly fishing on the Mac but not gonna be happening anytime soon. 
