That's called experience. You've got to earn your expert stripes. There are resources online that will help in this regard a lot though. B&H has some wonderful free videos. PHLEARN for digging into PS. Lynda.com, KelbyOne to name but a few.... yep, many of the good ones require that you spend some $$$ to get the training you want to advance and work towards mastery of digital processing.
Well, yes of course expertise comes with experience. That much is obvious. However, there is 3 levels of training. Let's say the Sharpening Panel.
Level 1: Tells you where to find the tool and how to move a slider
Level 2: This goes into gruesome detail on definitions of Amount, Radius, Detail and Masking mean.
Level 3: This helps you take the specific knowledge gained in Level 1 and 2 and apply to the general cases to target your experience in order to expedite gaining expertise. Some instructors can't do this because they can't articulate how or why they do what they do or like what they like. Somewhat gets into philosophical approach. Requires ability to separate "personal preferences"from "acceptable" results.
Think of Level I and II as Math instruction. Level III as Engineering instruction that takes levels I & II and teaches you how to apply it. My rule in college was always try to take math courses from engineering professors.
