Guitar practice - general techniques I know :) I got it from a book for piano practice but I don't remember it anymore. I think the best way to believe it works is to try it. For me it works much better than starting slow in most cases, but maybe not so for everyone. In any case, I don't think it can hurt trying with one passage!
What do the terms “arco” and “ten.” mean? @luser: Tenuto is not very well defined so it could also mean that in some cases, especially when used for every note in a passage. However, I would still associate portato or non-legato with that.