I second this. It has to be local. ASL very much differs from region to region, and it evolves quickly. Certain areas even have deaf conventions every year where they go over the changes that have happened that year.

Anecdotally: I went looking for Catholic prayers in sign language, specifically the Nicene Creed, and came across a video from a nun from Alabama. I didn't recognize any of the signs she used. I finally found a video by a Lutheran priest from California which had signs I recognized. It was odd, but I realized that that's how different ASL can be from region to region.

Also, I'd add to beware of books, and to only use college textbooks and books recommended by the deaf community. I once saw a book saying to add an "s" for plural. There's actually no plural in ASL.