I figured if I layered them on sheets of A3 copy paper I could work on a stack of blocks at a time, moving between sewing machine and iron easily and keeping the pieces for each block separate - like a series of jigsaw puzzles - and gradually building them up. (Off-cuts of batting or flannel would probably work just as well, but I didn't have these to hand and copy paper is cheap and can be reused multiple times).
Once all the pieces for the block are joined, move the whole sheet to another handy place. (In my case my extension table was sitting behind the machine not being used.)
When all the current pieces have been joined pick up the whole stack and move it to your ironing mat to press and trim.
The mini blocks are now ready to audition the next fabrics to be added.
Then each block can remain on the paper as further additions are made until it has reached the required size. (In my case 11 1/2 ")
As clear as mud? It's working for me - helping to piece quickly and keeping each block separate. As there are so many pieces of varying size it's not practicable to chain piece but this is helping me to avoid chaos,
PS: This is supposed to be on my 'Tips and Tutorials' page but I can't work out how to do it. Help!