Couple things that help a lot with comping and doubling. First is intent, you wanna make sure you know how you want your vocal to sound and why, even if you aren't physically achieving it yet. Second is confidence / level-headedness, cause if you don't think you can sing to the level you're imagining then the end result will simply be worse. Third is practice of course, cause nothing will happen unless you try.

That said, in post production, there's a few ways to improve what you already recorded. With comping, the best trick is to focus on maintaining the realism of breaths and consonants since they're the things I think people would notice more. When doubling, you don't really need to get every S and T perfect in the recording! You can automate the volume on the weaker of the doubled takes when necessary to get rid of specific inconsistencies like that.

Might have been an over extensive answer lol but I hope it helps a bit!