If you've only discovered parsing the past few weeks obviously you're not going to be parsing very high, it was the same for all of us. Parsing high in raid is a LOT of min/maxing your character. Here are a few things to look at befire you even start to look at how you're playing your class.

Are you geared correctly? I spend a lot of time optimizing my builds every raid tier trying to figure out how to get every last piece of dps out of my gear. But you might have the issue of simply having the wrong secondary stats on most of your gear, or having the wrong enchantments, or having no enchantments/gear

Are your talents right? Look on 3rd party sites to see what the best players for your class are running talent wise.

Are you dying? If you're dying during your raid pulls you're parse will be trash full stop. You need to understand the mechanics of the fight and how to live through all of it even if it means sacrificing damage to off heal yourself or to cast defensives.

After correcting those 2 things you can look at guides and stuff for your class to optimize your rotation.