What is your theme (if you want everyone to make a specific block type please provide a pattern to follow)?
Giant Churn Dash blocks. The tutorials can be found here and here.
What size block would you like (unfinished v. finished)?
24.5" blocks according to the tutorial.
Do you have any particular instructions for the fabric (don't use a certain color as a background, use some of every fabric sent, etc.)?
You'll be sent one patterned fabric ready to be cut utilizing the diagram in the first link, plus two pieces of background fabric. The large one will be cut the same as the print fabric and the smaller one (8 1/2" X 8 1/2") will be the center block used when piecing your final nine patch. Please note in the second tutorial that the HST's need to be cut down to 8 1/2" before sewing together your nine patch block.
Can members use their own fabrics, or should we stick with yours? If yes, should it be washed or unwashed?
Please only use the fabrics sent
Can members make more than one block if they are feeling inspired?
One block each will be plenty to make a large quilt and a pieced back
Do you have preferences for thread color (white/off white/etc.)?
Any neutral thread you have in your machine should be fine for the piecing.