This is from Ruby Jean's Closet's Sweet Cheeks Peasant Blouse--I've simply printed two of them and stuck them together. Ignore my wobbly lines. I'm really bad at mouse drawing! Notice how similar it looks to a one legged pant pattern piece? The top edge is part of the neckline, while the bottom edge is the bottom of the sleeve.
Now, once we have everything cut out, and ironed, we need to prepare the fabric. This particular pattern features gathered, puffed sleeves. Raglan sleeves are most common in sports wear and coats, but occasionally appear in dresses and blouses. In fact, I've never seen a blouse like this with anything but raglan sleeves. So first step is to sew in the casing. I'm the first to admit that I'm a lazy seamstress. I see no reason to spend an hour with a hot iron, singeing my fingers when I can spend a few minutes with bias tape to get the same result. Since this also has ruffles, we sew those on, too, and put the casings in the front and back of the shirt. There are matching seams on the front and back pieces, so we pin in the sleeves. In a lot of ways, raglan sleeves are easier than traditional sleeves, because we don't have to contend with the sleeve cap and setting in sleeves.
Once it's sewn together and the seams finished, the side seams are next. Every pattern with raglan sleeves I've ever seen would have you stop with sewing and finishing the side seams, but I know better. Story time!
My mother was born in 1945. That means that she grew up in a time where Home Economics was a requirement for girls, and sewing was part of the curriculum. (This was in the fifties, I think.) In school, one of the projects was a raglan sleeve blouse, which she made to the approval of her teacher... and the first time she wore it, she lifted her arms and the sleeves ripped out! She brought it to her mother, and Grandma laughed herself sick, fixed it, and then explained the problem. With raglan sleeves, there is a huge amount of stress placed on the seams. Which means that where they meet is where if you don't do something, it will rip out.
So first things first. We cut a rectangle of bias tape... Fold under the raw edges and pin over where the seams meet.
Next, we sew around it to secure it, and then I prefer to sew through it in an X from corner to corner. That reinforces the point of greatest stress. Now when you lift your arms, it won't rip out. By using matching thread, it doesn't really show from the outside unless you're looking, either.
Now all that's left to finish the blouse is the neck casing and hem. And remember, LAZY! Hello bias tape casings, goodbye burned fingers!