the best way to do it (in my experimental experience) is to do the first shine normally, then slide you thumb from y>b rather quickly (probably as fast as/ faster than you can). You can then repeat the y>b motion for additional shines (if necessary, usually isn't, unless you're breaking shields). You SHOULD NOT (if you're learning) slide your finger from b>y. because the Y>b slide actually does the full jc shine by itself in one motion, where b>y doesn't mean anything (just shine>jump, oooh, that's usefull when you're trying to double shine...). But the y>b slide is a modularized jc shine, so it can be used for all types of jc shining, like multishining, shining out of shield, or jc shining out of a dash.