I don't really have a chance to go against a real person to practice JJ most of the time so one thing I like to do just playin around is take a chair with four open legs no bars in the way on the legs or nothing, And climb under it and wrap my legs around the seat like I'm in the guard and mess around with dif movements like shin chokes and triangles, plata, Or do some funky spider pull ups while I'm in that position I grab the seat and pull my self off the ground and hold my self up for a bit..........Its pretty fun.
If I had a taller chair with longer legs I could mess around with some other stuff too :P
NOTE: To self I need to get me a big dummy to snap in half.