Mixing is one of those activities that's harder than it looks. Like skiing. You watch somebody do it and think "how hard can that be?". Then you try it yourself.
It'll be frustrating at first. Everybody experiences that. For most folks, it takes a good year or so of trial and error before they start feeling satisfied with their mixes.
And just when you're feeling good about your efforts, a strange thing happens: a second wave of dissatisfaction as you start to hear more and more flaws. That's your ears being trained to listen critically. The better you get at listening, the more flaws you hear. Fortunately, all the while you're also learning techniques to mitigate them.
And now the bad news: that feeling that the mix is never perfect lasts forever. I've been doing this for 50 years and it's still frustrating.
First step: take our Scottish friend's advice above and post your mix. It's a leap of faith to expose yourself to criticism, but you'll be able to leverage the experience of people like James and many others. Spend some time listening to other peoples' submissions. That will let you know which posters know what they're talking about.