Quick one. I just came across this post: How to make a muslin (also called a toile) on Sewaholic's blog. This is just fabulous.
She machine bastes along the stitching lines which I have done before and it is very useful. Even if you don't topstitch an edge (it's only a muslin after all) you can still see where it would be. The basted stitch line prevents the fabric from distorting. And it makes it much easier, and more accurate, to fold the fabric over and press into place for a better idea of how this piece will look.
She also stitches along the line markings for darts - now, I've never done that before but it's brilliant!
She explains that she does this for super clear accuracy: any changes you make to the muslin you can then apply exactly to the pattern. If you used a calico fabric you can write on it and those marked lines can be easily seen and compared to the basted lines of the original pattern. Genius.
Go read her blog post, there are follow-up pieces, i.e. a post about reasons for making a muslin.
I also liked the fact that she was making up the muslin of only the bodice to check for fit and didn't waste material and time on the skirt. You could if you want a wearable muslin out of the whole effort, but a non-wearable version that you can mess around with is good too. I would recommend it for difficult and complex patterns.
I am posting photos of the muslin I made of my jacket for the sewalong. I'm so glad I did: I found that I don't like the style at all. That was rather eye-opening. I'm so glad I didn't waste my previous black wool fabric.
At least it gave me the chance to do an FBA: it was great practice and also good to see that it worked well.