1. The vocal or lead instrument gets lost. Words get lost or the vocal seems buried during certain sections of the song. This is what automation is for. Go back and ride that sucker so every word can be heard.
2. There's a big frequency build up from adding EQ at the same frequencies to a lot of tracks. Everything sounds better with EQ added, especially when it's soloed. The problem is that if you EQ most of your tracks at the same frequencies, you'll end up with a lot of tracks that sound great by themselves that fight each other when added to mix. Better to do your EQing without soloing, or solo up several channels at the same time, in order to avoid the problem. And remember that you don't always have to boost the EQ. Attenuating a frequency can be more effective.
3. The stereo spectrum is mushy. This comes from taking panning for granted and automatically panning stereo elements hard left and hard right. When that happens it no longer sounds like stereo anymore and becomes "Big Mono" as my buddy mixer Ed Seay calls it. Just because a keyboard is in stereo, it doesn't necessarily mean that it should be panned hard left and hard right. The same goes for overheads. Many mixers intentionally stay away from hard left and right and try to give every track it's own place in the stereo spectrum.
4. There's too much compression. As the great engineer Joe Chiccarelli stated in my Mixing Engineer's Handbook, "Compression is like this drug that you can’t get enough of. You squish things and it feels great and it sounds exciting, but the next day you come back and you say, “Oh God, it’s too much.” Sometimes you have to really squash something so it works in the mix, but usually a little goes a long way.
5. There's too much low EQ. It's very easy to get fooled into thinking that you don't have enough low end either because you're mixing on small nearfield monitors or you're mixing too quietly. When that happens, you'll find that the mix sounds great in your room but way to boomy everywhere else. Take a listen to a recording that you really love first to see where the low end is at or take a look at a spectrum analyzer before you add any.
If you want to get some great mixing tips and tricks, check out my 101 Mixing Tricks coaching program and get 4 free tricks right away.
Don't forget to check out my Music 3.0 blog for tips and tricks on navigating social media and the new music business.