Hum... I don't have so much experience but I can give you some tips I found mapping AND jumping (it's really personal, other jump mappers may proceed differently and disagree with my jump experience):
- When I create a jump
1. I have the jump in mind so I just map it and I test it (just simple brushes and textures: I just want to fix distances here)
or
2. I don't have the jump in mind (douzejumps

) but I have some plateforms shapes / general ideas in mind and I try to make something
- You have to finish (talking about jump skills) your jump map and not to depend on an other (pro) jumper !
- No randomness in your jump ! I made some stuff with a circle shape to gain speed but you had to hit the correct angle and this is so annoying for others...
- Connect you jumps with corner corridors so you don't have to hint you map

- Don't make it too hard (except if you wanna make the hardest map ever !) if you wanna convince more people.
- Difficulty should (has to!) increase.
- IMO, lighting is even more crucial on jump maps than on standard maps. Atmosphere (for me) is really important on jump maps, and honnestly, there are only a few really good jump maps (atmosphere).
I wanted to talk about spawn, lemming,... but I thought about X-RaY's post:
http://www.urtjumpers.com/forum/viewtopic.php?id=918.
To conclude (I don't like long posts...), I'd say there are several kinds of jump maps: old school, realistic, outdoor,... / unique design, multiple design... so choose your style (or create a new one !) and
enjoy you own map !