The glossy eyelid look you've been seeing everywhere is actually pretty simple to achieve! The easiest way is to put a tiny dab of vaseline on your eyelids (you can pick some up here). You could also use plain clear lip gloss, which gives off even more shine, but will have a stickier feel to it. If you want to add gloss over top of an eyeshadow, keep in mind that the gloss will break down the eyeshadow and it will migrate & crease. The best way to combat this issue is to start with a waterproof cream eyeshadow (like this one from Make Up For Ever) rather than a powder shadow underneath the gloss, as it will break down less.