Eyepiece selection: Spacing, rules of thumb?

I've read different "rules" for selecting a set of eyepieces--e.g.,

1) low, medium, and high power

2) exit pupils of 4mm, 2mm, and 1 mm (e.p. = eyepiece f.l./ scope f.l.)

3) spacing them (& a barlow) so that each has a magnification of 1.4-1.5x the next one.

What do you recommend, and what is the spacing of your most used eyepieces?

If someone were buying a set of 3 eyepieces and a barlow, what would you recommend as to their spacing?

Larry, under item 2 in your message you state that the exit pupil equals the ratio of the ep focal length to the scope focal length. The exit pupil is really the ratio of the scope diameter to the magnification. This quantity reduces to the ratio of the eyepiece focal length to the scope F number. The dimension of this ratio is distance, mm. The ratio that you stated is dimensionless which indicates some kind of error in the expression. Try a few calculations with each expression and the one that I sent will give you pretty accurate numbers.
Ted