I grew up in New England, fishing both salt and sweet water. In either waters, I am forever thankful for all fishy experiences I have had -- most especially to the people who provided and/or shared theses experiences with me. I am also grateful for the thousands of mistakes I made along the way (I do mean thousands -- I am 100% self-taught). When I think of my errors, e.g. back casting a fly into a stream side tree (not once, but two times in a row), I am thoroughly embarrassed. Decades have passed since that time, and that New England boy is now a roll casting expert (i.e., no more climbing trees for flies).
In northern Colorado, you have many fly fishing and fly casting class opportunities. My recommendations to beginners:
1. Take as many free classes as possible. For example: Colorado Parks & Wildlife
Note: Many free classes at retail stores are designed for you to buy product (not judging, but could be good, neutral, or bad for student/consumer).
2. Go make mistakes -- climb trees!
3. Feel free to read info on this blog: Equipment Info
4. Use my blog search engine, e.g., type in nymphs, or nymph rigs (there are hundreds of educational posts)
5. When you have exhausted free classes, and have climbed many trees, maybe it's time for fly casting lessons USA Lessons
Why FFI instruction? Casting Instructors are trained to teach (i.e., many guides are excellent guides, but average teachers). Find an instructor near you Fly Fishers International
6. Class Size: Arguably the most critical information for beginners and consumers.
For the very best education, research supports small class size! Many industry classes are packed with students and one instructor only = it's a poor educational/teaching model, but highly profitable. I have seen +20 students in a class (e.g., 20 students X $100 = $2,000).
Hope this info has helped, and good luck with your fishing journey.