Basically I'm just curious as to how long it took you experts to get improvising down? :)

I already know what they will tell you... so, I'm taking the liberty to tell you myself. Improvising is a lifetime learning experience. You never stop learning to improvise. Just like eartraining and all those other nice skills :)

Just play what comes out, it doesn't have to be perfect just something. As with all things practice makes perfect.

A few exercizes you could try are:

1. Play the most random thing that comes to you for 5 minutes, all the while developing the melody and find out what sounded good to you or others.

2. Set out a certain chord progression and then practice a walking line to connects these chords while improvising fills or variations to the melody. Don't be afraid to change key, tempo, time signature, technique, make a mistake, or sound noodley. Sometimes a good melody will come from the most unlikely places.

Record yourself playing if possible and then study the parts that you like and identify why you like them.

Good Luck

gbf is right - it's what keeps Jazz players interested for their whole lives and I would be very surprised if any experienced Jazz player said they had ever "got improvising down" !! ;)

It is something you learn more about, all the time and never stop!!

IMO abark000's exercises were great... I've been having some problems with improvising solo's and that's just what I've been doing and it helps a lot!