I made a huge mistake and for many years worked with bad monitors.  I never considered myself a mixer, but a composer....still should have had better monitoring.  A big client of mine downsized and I picked up a used pair of Yamaha HS5s for 200 bucks at an auction.  What a huge difference.
 
One other thing I stumbled upon.  A friend built me a sound blocking stand thing to put behind or around a mic to block reflections.  It is about 2.5' wide and 4' high and stand about 6 feet tall on the wood frame he built.  I have found that by placing it directly behind me while mixing makes a big difference.  I can work very effectively at very low volume levels. 
 
I guess the point I'm getting at is ...good monitors in a good mixing environment makes thing a lot better.  Wish I had done this years ago.  
 
 

+1 to ARC2!!

John
Using near field monitors is the only way to mix. Use headphones as a supplemental check.  

I use a good pair of headphones to do my initial mixing and mastering (so I won't drive my wife nuts hearing the same song over and over again). I use a "Redline Monitor" plug-in that emulates near-field monitors by mixing the correct amount of left signal into the right ear and vice-versa. I always end up with something that sounds great on the monitors.
Walt

Jimbo 88
I made a huge mistake and for many years worked with bad monitors.  I never considered myself a mixer, but a composer....

Same here.  I thought that given my tiny, acoustically challenged space that I would never be able to get a good sound with monitors… didn't even know what "near field" meant. I do now, and I'm now more inspired to explore the acoustic treatment of my space further.
 
Rob

rcrees

Jimbo 88
I made a huge mistake and for many years worked with bad monitors.  I never considered myself a mixer, but a composer....

Same here.  I thought that given my tiny, acoustically challenged space that I would never be able to get a good sound with monitors… didn't even know what "near field" meant. I do now, and I'm now more inspired to explore the acoustic treatment of my space further.
 
Rob

Agreed with the sentiment in this thread. Having monitors makes a world of difference in being able to get a mix to sound like it works in other places than your own set up with headphones. Monitors really help reveal where tweaks to the mix can make it sound better overall.

 
And don't forget to take a stroll out in the hall and see what it sounds like from there.

Adam f5 is the pair that changed my life of mixing