Well, I don't know why I didn't write this earlier...
4 things are a MUST and the 5th is optional:
1) Adjustable seat height: Knees should be just barely lower than hips. The angle at your hips should be about 95 degrees (just a smidge wider than a right angle.)
2) Adjustable seat back: This puts the back of the knees about three fingers in front of the front of the seat. If we sit too far back, we slump to reach the machine/work. Have you ever been bothered by cutting off the circulation at the back of your legs against the chair? (can't remember the other details on this point ) :-( sorry...
3)Adjustable seat back height: "Don't cover up shoulder blades." The support should be in the middle of the back. We should be aiming for maintaining the normal curves in the spine. A quick google search will help with this?
4) The arm rests should be short, stubby arm rests. Too long and we can't maneuver the chair to the correct position at the machine table... makes us lean forward putting strain on the back and neck.
5) A really nice chair will have a seat tilt... but should not be more than 5 degrees forward. He mentioned that tilting the machine is an option, too... just pay attention to your body when you make a change.
One thing he said about preventing fatigue and strain is to get up every 10-15 minutes, walk around, stretch out. And remember, stretches should be long and sloooooowwww. 10-15 seconds on each stretch, at least! This is one reason I have the ironing board close by, but not right next to the machine. Of course, I'm thinking a little treat from the kitchen is appropriate, too, occasionally!
He gave some exercises, but I'm afraid I won't explain them correctly and you might be worse off! Again, a google search for stretches done at the office will probably give you some good ideas.
Hope this helps?