Well, there are four methods I use depending on what type of meat: rubbing, marinating, brining and injection.
Rubbing is pretty much universal, but I do tailor the rubs for both the meat and the expected final prep. Allowing the rub to penetrate a bit (six hours to overnight) while wrapped and refrigerated seems to boost flavor.
With regard to marinating, I love this method for thin to moderately thick cuts and I'm a fan of reducing the salt a bit and doing an overnight marinade. This works when I want particularly strong flavors rather than the "meatiness" to be the star.
Brining is used when I want to simultaneously boost moisture and flavor. Any poultry and a lot of pork get this treatment from me.
Finally ... injecting. I know many purists will reject this out of hand but pumping a brisket or big pork butt are great ways to quickly increase internal flavor and moisture. I usually inject, throw in the fridge to cool the meat back down and then go in the smoker about an hour later.
Everyone will have different methods but a good rub after a good brine is pretty much bulletproof for flavor enhancement ...