It's all about vectors masks and layer styles. Wanna make a sweet glossy button? It's just a simple rounded rectangle vector mask with a gradient fill, drop shadow, inner/outer glow and texture overlay.

Also learn about blending options/modes (i.e. screen, multiply, overlay, etc.) for combining effects.

Also subscribe to the RSS feed of 365psd.com, download each day's psd and figure out how it works.