Sleeves are the bane of my costuming existence. I hate easing. I hates sleeves, yes I do. A friend of mine called them "sleevil", which is an appropriate term for them; sleeves + evil = sleevil.
There are many instructions on how to do set-in sleeves (for example, Craftsy has a photo tutorial), but regardless of who writes the instructions, the actual reality of setting in sleeves is much harder than what most of the deceptively easy instructions would have you believe, especially when there is a lot of extra fabric in the sleeve that needs to be eased into the body.
There are techniques & tips that make things "easier", such as ease stitching, a tailor's ham, and the copious use of pins. (There are "cheater" methods for setting in sleeves (like this one), which I've used for very simple garments, like shirts, but that don't work with highly tailored or more complicated garments, like the one I'm making.)
I tend to use a combination of all three of the above mentioned techniques to get a decent ease. First, I add 3 lines of ease stitching along the sleeve cap to start the easing process.
Then I pin all the appropriate markings together to anchor the sleeve and set the endpoints for the easing.
I use a ham to help the easing process around the curves. Most people use a tailor's ham to press curved seams, but they are extremely helpful in easing too. (You pin parts of the curved
area to the ham, then start pinning fabric together)
ham holder made my life much easier when using a tailor's ham
I use a bajillion pins when easing the sleeves.
From personal experience, hand-basting sleeves is much more efficient than trying to machine baste, especially with so many pins sticking out of the sleeve. It's also easier to slightly shift the ease around with hand-basted stitches with your fingers. (Once you're happy with the handbasting and have removed the pins, you can machine stitch the armscye.)
However, despite all of these precautionary methods , I still find myself having to "redo" sleeves several times over because the sleeve is just not set-in correctly and there are obvious bumps, tucks, and wrinkles. And this costume was no exception. A one point during the construction of this jacket, I actually became extremely frustrated and turned to my Viking for help, since he's much better at setting in sleeves than I am.
We'll see how well I manage to ease in these sleevils.....