Brining and injecting a butt

Bill:
I’m one of your BBQ Book subscribers and, I hate to admit, am just now doing my first butt on my Traeger.  I saw your suggestion to inject it and I bought a low-priced Cajun Injector (they have several models up to about $30 in my store), and also noted your recommended ingredients to inject – apple juice, soy sauce and Worcestershire sauce.  But in what proportions?  Your book doesn’t say.  And if I have time to brine the but overnight, what would be the solution I should use for that?
Many thanks for the reply.
Chris