If one wants to use shorter lines, one thing is needed (as above responses show):
Tell yourself you WANT to learn to ride shorter lines, and only use these for a very long time!
As all your timing and backbone transition experience has to be re-learned.
But it will come a lot faster of course, than when learning to foil - but important not to be let down by the initial "This simply doesnt work" feel we all got when changing to shorter lines
So use a lot of time to see if you prefer the shorter or medium (normal for non-foiling boards) or a bit longer lines (assuming really long lines 30-32 meter only to be for really low winds)
Not many use shorter lines, but a few of the good riders like Frank Rosin does, and I think it is both with foil and LEI kites
Racers use shorter lines, but this is to be able to manage bigger kites, so not relevant for free/waveriders.
I have taken some time myself to get used to shorter lines (for me, shorter lines is the std 21-22 m lines on my wavebars), so I got the timing right, but I still did not like it I must say, and went back to 26 meter for all kitesizes in normally powered conditions.
Even in waves I can just fly the kite a bit higher and turn it back and forth, so not slower than shorter lines (like it would be on a surfboard where you need more pull).
Some prefer the shorter lines, so I am also curious as to why, as of course there are advantages?
Frank, you would be able to tell why you prefer the shorter lines, ups and downs of these?
Interesting to hear about experiences with different line lengths for "general riding", especially from those having taken the time to get used to them