[Harp-L] Memphis Blues

[Pic2318834@xxxxxxx]

Hey,
I just got back from Memphis.  My first jam with a band, I got up on stage 
after they saw me with my harp out in the background and talked me into playing. 
 Boy was I a nervous wreck but played basic 12 bar blues and think I did ok.  
My problem is this.  I never know what to play when playing lead,  I know 
most riffs playing alone with songs and doing background to it, but when its an 
improve jam my brain goes numb and I forget most things I can play.  Any help 
out there as to how you decide what to play when you get up there?

PIC