The strips can be all lengths, I cut some of my longer ones down smaller as I am making a smaller project and not a full size quilt,
Then you attach all of the same fabric strips to make one very long one, (if you have a lot you can always do more than one,
I just do the grab style, if you are doing more of a planned thing you will do them in some sort of order, I just try and not grab to similar a color and not the same one to close together in the strip