My rig is set up in a spare bedroom that is about 15' by 15' (somewhat irregular shape).  Most of my work is mixing stuff that was tracked elsewhere.  If I do any recording in that space, it is just a single instrument or sometimes several singers.
 
So my priority is on hearing the material accurately.  I have been using a pair of Yamaha MSP5 monitors.  These are very nice 2-way speakers with a 5" LF driver.  I think they are intended for near-field placement.  Mine are actually set on some shelves across the room.  The left one is 9 feet from my ears.  The right one is 10.5 feet from my ears.  That gives a stereo imbalance, but was necessary because of the doorway.
 
I'm looking to improve my monitor setup.  If I went with larger monitors, the only way to mount them symmetrically would be to fly them from the ceiling.  That may be a bit much at this stage.  I could get some floor stands to mount the MSP5s closer to my workstation.  That seems like the easiest way to make a quick improvement.
 
So my question really is, when using these smaller monitors, what is the ideal placement, distance from ears and separation left to right?  Any insights and opinions are welcome.

I would look at some monitors with a minimum 8 inch woofers for near field monitors. The tweeters can be just about anything as long as they sound good to you. For near field monitors you need to have them set equal distanced from your listening location. They should be angled toward you. One thing to keep in mind about near fields is they have very narrow dispersion in the higher frequencies. Regular loud speaker try to have as wide dispersion as possible to fill a room. Bass frequencies generally are non directional. Transients usually have a high frequency component that gives direction. So bass with a sharp hit to them will have a location.    
 
You may need to treat your room with acoustic bass traps and absorbent treatment to lessen echoes. Try to avoid standing waves where your primary listening location is. If the room is oddly shaped that can either help or exacerbate standing waves. BTW standing waves are acoustic waves either reinforced by being in phase due to reflection or diminished from being out of phase for the same reason.
 
These are just general guide lines for setting up monitors. This subject is huge and can't be fully discussed on a forum.  

John's got the basics right. The MP5s are nice speakers - major studios will use them as their nearfields.  But you need to be closer to them if you are to get any sense of bass.   Ideally, your speakers and head form an isosceles triangle.
 

Get your speakers as close as possible to your ears,if you have to use speaker stands thats great,use a peace of string to measure from the center of the left speaker cone to the center of the right speaker cone,then with that measurement stretch the string out from the center of the left speaker to where your left ear would be,then the same on the right forming an equilateral triangle.make sure your tweeters are level with your ears. this helps me alot hope it helps you as much.

AT
But you need to be closer to them if you are to get any sense of bass.   Ideally, your speakers and head form an isosceles triangle.

Can you give me a rough idea of how close?  With my furniture arrangement, it would be easy to use floor stands such that each speaker would be about 35 degrees off center and about 3.5 feet from my ears. 
 
The only drawback to that is that if somebody else is working with me on a mix, they wouldn't be in a good place.  But I guess I could re-position the speakers a little in those cases.

Any more than about 5 feet away and you're in dangerous territory.
 
I'd say between 3 and 4 feet is the optimum distance

I have tried many different speaker arrangements (distance wise).
I have tried the 3 triangle, ive tried the 5 - 3 spread triangle
But(and this is important) *The tests that I've done in my room, I have found that a 6 ft spread, at approx. 3.5 feet away works perfect. Not sure if anyone mentioned this yet...but the speakers are at ear height. 
My Control Room is 8 feet wide by 16 feet long. The spears are set up to travel the distance of the room, not the travel the width. I also have several sets of speakers for A/B comparisons.
My speakers are wired with Balanced cables (XLR) and each set is patched in to a 16 port patchbay.
This is so I can switch speakers out quickly for different listening environments. as well as Stereo, Mono.
 
Room treatment really helps as well. if I had to suggest anything to start with, it would be bass traps.
However, this is not always practical in a house, bedroom setting. so any good sound foam will do.
These need to be placed strategically.

Yep, bass traps in the corners are rhe first area to be treated.
 
If you can, then start on the mirror points.
 
Get a willing accomplice to slide a mirror on the walls to your left & right as you sit in your chair. When you can see the speakers reflection, that's your mirror (first reflection) points
 
After that maybe a ceiling cloud, angled slightly up/away from you as it goes backwards

Do have room for speaker stands? That could enable you to a) get the speakers closer to your ears, b) get them properly triangulated, and c) get them as far from walls as possible.
 
I'm not sure 8" woofers will really do that much for you. In a large room with acoustic treatments, yes. But in a mostly square room, deeper bass response is likely to compound your problems.

I appreciate all the ideas.  I'm going to install speaker stands today and get those speakers closer.  That should help a lot.  Then I'll start planning bass traps.
 
One problem with my arrangement is that there is a large window and glass door right where the speakers will be aiming.  It would be a major undertaking to move the furniture around, and I like the karma of working by that window.  I don't have drapes -- I use blinds -- and to preserve domestic tranquility, I probably cannot alter the window setup. 
 
I am thinking about locating sound traps on the perpendicular walls where sound would go after reflecting off the glass.  Does that make any sense?  I should also mention that the room is fully carpeted and has a lot of instruments on shelves on every wall surface, so most of the walls are not exposed as flat surfaces already. The ceiling is textured, which also probably helps a little.
 
Most of what I do is jazz, so it doesn't have as much of the thundering bass and kick drums as other art forms.  We do get some strong bari sax and bass trombone vibes though.