Draw a square , that will be the size or shape of your finished background so it really depends on you what size and dimensions do you want it doesnt really matter.
Click and select mesh tool , here we would like to add a little light into the background so selecting a colour lighter than the shade of your selected background colour will give it a nice glow .
You dont necessarily have to use presently available brushes , here the ones i am using are available to download from the site as well you can get them here! .
so just select the brush of your choice and using a pencil tool draw some swirly shapes on your work board.
Select the lines drawn , use a brush adjust it draw more lines slect anyother brush adjust it , keep playing until you get something interesting.
Now the background seems a bit too boring lets give it a little bit of life use the pen tool and draw a wavy path somewhere .
Now repeat and draw another path but with a different kind of wave
Select both paths go to OBJECT>BLEND > BLENDING OPTIONS a window will pop up give some specified steps say here i have given 25 then hit ok!
Select stroke colour go to object>BLEND , so you will get something like this!
Choose paint brush tool pick up any othe scatter brushes and start playing around .
It Really depends on your own creativity that how you accomplish this here is my finished product i would love to see what you come up with!
you might be interested to know how it is done in photoshop?