I hate knitting sleeves separately, so whenever I can, I knit them Tandem- 2 at a time on a circular needle, in a single piece with 10 stitch steeks in between. This works for any sleeve pattern, not just Fair Isle, as long as you're using yarn with some *grab*.
Cast on and knit the cuffs back and forth (not in the round) separately (so they don't have a bulky seam), and then join them, casting on 10 stitch steeks in between the sleeves on a circular needle. Knit as per the instructions, working the steeks in alternate colors on 2-color rnds. Bind off.
Click on any of the images to enlarge them.
#1. Finished sleeves, still in one piece
#2. You can use any sort of steek reinforcement method you prefer. I like to zig-zag stitch on either side of the center steek stitches. You can be brave and just cut the steek open and reinforce later, but I don't recommend doing that on your first steek.
#3. Steek reinforcement completed.
#4. Cut between the lines of zig-zag stitching. The stitches won't go anywhere. Trust me. (sorry for the blurry pic. I didn't realize it wasn't sharp until it was too late to take another).
#5. One steek cut. The other needs to be reinforced and cut.
#6. Sleeves separated.
#7. Inside view- just because I think it's pretty.
#8. Fold the steek edges in and sew the sleeve seam. This method does add some bulk to the sleeve seam. On the other hand, you don't have to weave any ends in, so it's an even trade. In case you're wondering, I didn't bother trying to make the motifs match at the seam. If you want nicely blended motifs, just center each set of sleeve motifs, and they'll work out.
#9. Whip stitch the steek down. I usually use a yarn or thread color that blends in more, but I wanted the stitches to show for the picture.
#10. The seamed sleeves are ready to sew in the armholes.
Except that the armholes aren't ready for the sleeves.
I'll post tutorials on cutting armholes without steeks, and neckline shaping as I get to those stages on the sweater.