One of the biggest issues musicians face when trying to give a final evaluation of their songs is that by the time they're close to being finished, they've probably heard the song in question literally hundreds of times. It becomes very easy to lose your focus and misplace what's important and what isn't. So, to be able to give your own music an objective listen, the key is to lose some of that familiarity. How do you do that?
• Take a Break
It's a good idea to take frequent breaks when working on your music anyway, as your ears, especially at loud volumes, tend to get fatigued. But beyond that, when you've listened to a song over and over, you often begin to lose your ability to judge what works and what doesn't. So take a break! At the very least, get up and do something every couple hours or so. Eat lunch. Go for a walk. Run some errands. Anything that gets you out of the studio for a bit helps. Ideally, if you can go a few days without listening to the song, you'll find you're much more able to come back and listen to it with fresh ears.
• Turn Your Monitor Off
It's amazing how much the visual feedback in your DAW can impact how you hear things. Try turning off your computer monitor and just listening to the music without the visual stimuli. Hell, just close your eyes and listen. You'll be amazed how much more focused your listening abilities become.
• Listen Outside Your Studio
By now, you're probably very used to your studio as a listening environment. And that's good! The more you know the sound of your studio, the better you'll be able to mix. But if you want to shake things up and listen to your music from a new perspective, burn it to a CD (remember those?) and go listen to your music outside of the studio environment. You should do this anyway to ensure that your music will sound good on a wide variety of sound systems, but hearing your songs outside the studio can be very helpful in letting you hear them in a different way and can help you pinpoint potential issues.
• The "Behind Closed Doors" Listen
This is a somewhat unconventional technique that I've found useful in honing a mix. Simply step outside your studio, close the door, and listen to it in the next room. It needn't be blasting, just loud enough for you to hear it. For me, this helps me hear the track as a whole instead of picking it apart into each little part. It's really the only way I can get back to listening to music the way I did before I was a musician. Big problems that might not be obvious after getting used to a mix usually stick out to me more when I use this trick. Instruments that are too loud or quite often sound more obvious from the next room. Your mileage may vary, but I've had good results from this.
• Get a Listening Buddy
If you're a musician, especially in this day and age, chances are you know other musicians. Find someone whose production and ears you trust and become listening buddies. Have an agreement that they'll listen to a track whenever you need them to and return the favor. Agree that you'll both be brutally honest and that no one's feelings are going to be hurt if the feedback is negative. It's much better to find out about those problems now than when you release your album to the public. With the ease of sending files over the Internet, there's really no excuse NOT to do this. And if you're a bit of a lone wolf? There are tons of forums online where you can post your works in progress and get feedback. This isn't quite as ideal since you don't know the backgrounds of the people listening, but as a last resort, it can still be valuable in honing in on your weak spots.