Distance fly suggestions
When I wanted to start fly, the first thing I did was pickup the Bettterfly DVD. AWESOME breakdown of the stroke in stages with tips for relaxed fly (like I do for distance), and speed fly (racing or more flexible folks). While I "got it" at first and was able to do the stroke, I never "got it" to the point that it was relaxed and fluid. I first worked on deepening and lengthening my glides and got down to about 4 strokes per lap without initial kicks, but very slow, and couldn't maintain it due to running out of air. Terry recommended I increase the stroke count to get more air, and that helped a lot, but I still wasn't in a kaizen mode.
A swim buddy showed how he did 1-arm fly practice to smooth out his body wave. I added that to my freestyle for a few months. I swam with one arm extended forward like a skate position, and did the fly movement with the other arm and switched arms each turn (usually facing the best scenery in the pool of course). A couple of months like that and I went back for a review of the Betterfly, and then in the middle of a lap of 1-arm, I rolled into full fly, and then kept it up for a mile without significant effort! I tend to breath on almost every stroke, and do 7-8 strokes per lap. Since then I've been able to get up to a 5K distance in fly, breaking every 10 laps or 15 min for a quick drink. I don't know how folks like Diana Nyad can go 90 minutes between hydrations!
Concentrate on relaxation and a snake or dolphin like mindset as you undulate your body. Flow with the water.