What is the best way to learn a signed language as a second language (L2)? The bad news is that there is none.
But, the good news is that there is. The best way is actually a combination of the learning strategies: listening and practicing with a native signer, immersion, ASL classes and a few others. Below are some methods that you can combine them that work best for you or your learning style.
Immersion in a ASL/Deaf community and its culture is one of the most efficient ways of learning ASL or another (sign) language. Why?
Context, context, and context. Socialize both in open (public) events and in private gatherings with native- and fluent-ASL friends or family.
Learning a language is not without learning its culture, including norms, values, history, communication behaviors (turn-taking, attention-calling, naming, social introducing, etc.), and most of all grammatical rules of ASL. Take notes of syntactic grammar, facial grammar, inflections, tones and variations from native ASL signers in endless various contexts.
Take a face-to-face ASL class in your area. It helps you understand the structure of ASL. Interaction with a qualified instructor is also important that the instructor can offer you feedback as well as help correct your sign production (equivalent to pronunciation).
If you consider a career in ASL-English interpreting, seriously consider a out-of-town study, if necessary, to take a good-reputed program of ASL and Deaf Culture Studies and further another program of ASL-English interpreting.
Online materials such as ASL dictionary and articles are a wonderful convenience and quick access. These resources are useful for homework and self-learning, but check for reliable sources.
Learning ASL solely from online isn't the best way, but it's useful for an educational entertainment or informal learning, curiosity or exploration.
Hire a qualified native-ASL tutor if you wish to improve your weak area in ASL grammar or vocabulary. It may cost your pocket but it's worth pulling up your marks in your ASL or interpreting courses.
Alexa Payne's straightforward statement reads "If you don't want to learn grammar, you don't want to learn. Period." If you'd simply rather learn ASL vocabulary and use English grammar in it, you're not actually learning ASL. Embrace grammar.
I know grammar could be a dry subject, but it's actually fun in ASL. Because, grammar in the spatial-visual-kinesthetic environment is different from the spoken form.
Respect the people of their language and culture. Practice ethics and respect. And, not only you will be respected back, but also you will be embraced into an ASL community.
Also see learning strategies in classroom
Tips on learning immersion in sign language.
benefits of no voice policy in learning sign language.