In my opinion, the main thing for an envato author to keep in mind is understanding other people’s feelings and needs. In other words, you have to develop empathy, if you want to be successful here.
Try to predict how your client would use your tracks, how your tracks could support his projects. For me it’s a kind of difficult task, especially if you used to make music to express yourself and not to align it with other people’s projects.
I agree with the previous guys, that the mixing of your track is not a problem here. If the reviewer rejects your item, and it is not the mixing/mastering issue, he might just not clearly understand the ‘message’ of your track, i.e. how a potential client would use it. I think the reviewers here in most cases have a really good sense of what will ‘work’ and what won’t, so even if such track passes the review, you might not have any sales on it, because people couldn’t understand its ‘message’ as well, even if they like it. I can tell it, because I still have such tracks in my portfolio
Just don’t give up, try to listen to library music labels to better understand the ‘moods’ and ‘messages’ commonly used in media, always keep in mind that audiojungle isn’t a service like iTunes, where people buy music to listen to, but it is a library: you search music by the moods/tags/categories, then you choose what will work for your project.
Hopefully, you can get what I mean, as english is not my native language. Sorry if my reply is a little bit messy.
The reject is just a beginning!