I like to do a couple of blocks completely to make sure they are the correct size and colour placement. If the blocks are going to have sashing the colour placement doesn't matter as much. Sometimes if it's a repeated block, I like to see how the colours/pattern will look as they are put together. If there is no sashing, I will sometimes change the colours so they are not blending the blocks and other times I like the secondary design of the blocks blending. After I have all the bugs worked out, I will chain piece them a row at a time.