I'm sure it's been addressed, but speak to me like I'm seeing a bike for the first time.

Relatively new bike+apex group+suspected cable stretch.

Basically the rear derailleur double shifts when I upshift (to a smaller cog). Looking at my rear dr from the back, which way to I turn the barrel adjuster, and how far? Also, my front dr rubs when I'm on the small ring, is there a barrel adjuster for that?

Thanks for the help - I'm getting tired of going to the LBS for minute adjustments that I should be capable of myself.