I usually spritz with a 1/2 and 1/2 mixture of Old Grand Dad and apple juice, until the internal temp gets to 165-170. I then foil it. Before sealing it up, I dump the remainder of the spritz mixture in, then seal. That way, you get a hint of the flavor you're looking for, not a full blown holy-chit-that-tastes-like-whiskey flavor you'll get from injecting.
Don't get me wrong, there's nothing wrong with injecting, but think about what juice and how much you are injecting into the meat. The flavors you put in, for the most part, stay there.
Hope this helps!