First, let's take a large t-shirt, like so:
The first step I use in resizing tees is cutting the sleeves off, with shirt inside out. Make sure you cut the serged seam line off as well, leaving the intact shirt with a clean cut.
Next cut the sides of the shirt, inside out works best. If the shirt has a seam be sure to cut that off as well, if it doesn't then just cut a straight line, until the shirt is just connected at the shoulders.
Take the shirt that fits you nicely, and compare to the dimensions and shape of your large tee. You will figure out from here how much to cut of the sides of your tee. Keep in mind the stretchiness of your liked shirt in comparison to the large tee, and leave plenty of room for adjustments. It's better to have your reconstructed tee too big at first than too small; that latter is harder to fix.
Put your nice shirt on top of your large one, and match the shoulders together and compare. You'll probably need to cut a good one or two inches from the shoulders, but leave some seam allowance and room for adjustment, as I did.
From there, I continue to compare the two shirts as I scoop out the shoulder seam and the room for the sleeves.
Once I do that, to make the cuts on both sides even, I'll fold the shirt over and then cut the excess material off the other side in comparison to the side I've already cut.
Now you have reduced the shoulders, you should probably reduce the sides. Just compare to the nice tshirt, leave room for seam allowances and then some for error. Once you take enough off the sides, you'll turn your shirt inside out, and sew the sides up like so:
Once that is done, I suggest putting the shirt on to see if you like the way it fits. I thought it was still too baggy, so I took the seams in some more, and I also didn't like how wide the shoulders still were, so I cut a little more off.
When you get it to your liking, you go for the sleeve adjustment. You can compare it to the shirt that you like, or make it in a different style. I did a little of both. I compared the sleeves by seeing how wide and long I needed to make them, and cut them accordingly.
I actually adjusted one sleeve, cut the width some and then cut some of the length off as you can see at the bottom, and then I put the cut sleeve on top of the uncut and cut around it to make them the same:
When you've cut the sleeves length, you're going to need to resew the sleeve back together to make the tube. When you've done that, compare to your shirt and make sure the sleeves aren't too big or small... mine were fine:
If they're too big, just adjust the seem some, if they're too small, you can either stretch to fit when you sew, or sew the side seams of the shirt smaller *tongue twister*
Now here comes actually sewing the sleeves. It's tricky to explain but once you try it one or two times you'll understand. FOLLOW:
Turn the sleeve inside out. Turn the shirt inside out.
You're going to match the right sides of the sleeve to the rights sides of the shirt, and pin them together.
Be sure to match the top of the sleeve (it usually has a crease) to the seam line of the shoulder.
Be sure to match the seam line from the sleeve to the seam line on the shirt, like so:
With the right sides matched, but the wrong sides facing out, you're going to sew the sleeve to the shirt, making a complete circle around the sleeve. Sorry there aren't a lot of pictures my digi cam was dying here. You'll do that with both sleeves, and you'll have this! :
Though it doesn't look smaller, since it was I could take the picture closer to get the whole shirt in... so yay!
You can always make small adjustments here and there, by just taking in more seam, or sewing the sleeves smaller, even if they are attatched to the shirt. Your shirt is hardly ever perfect the first time.
THAT'S THE HOW TO RESIZE A TSHIRT TUTORIAL! NOW FOR THE BAND/RIBBON/COLLAR TUTORIAL!
So you have your resized shirt and you like the way it fits. Now, you want to have a different color, or you want an off the shoulder top, your you want the sleeves to have trim. Well this method will work for all of them! Find a fabric that's knit or ribbed, that's like tshirt material, that's the color you want:
I want a different colored collar, so what I'm going to do, is cut that collar on the shirt off!
Also, I want the neckline to be a little deeper, so I'm cutting some material off the front! If you're doing an off the shoulder, you would do a wider scoop out of the shoulders as well.
You got the neckline the way you want it, and now you need to figure out how much material you're going to need for that neckline. Since the back is going to be the same, I just used the collar I cut off for the comparison.
What you'll need to do before cutting it out is double the how thick you want the collar to be, like how they do:
Then be sure to have about a centimeter seam allowance. What I did was lay the back collar I was using on top of the new fabric, and cut out the same exact shape from the red fabric. To get the new scoop line, I compared the back collar to the front one, and centered it... I could tell, just buy eyeing, you could use a tape measure, that I needed about one inch on either sides to make that material match up to the seam line. So when I cut out the front piece from the red, I added two inches on.
You'll have two pieces of thick red fabric. You'll need to connect these. Match the ends of both pieces together, making sure the right sides are touching eachother, and then sew.
Do that with the other end, and you'll have a connected circle like this:
Now, compare to the neckline on your tshirt and make sure it looks like it will fit. If it looks too big, MAKE IT SMALLER! If you don't, you'll have a floppy collar that looks stupid. If it's a little too small, that's no big deal, you can stretch it to fit and it looks cute too.
OK! For attatchment.. this is where you can make it look pretty professional. Take your collar material, and have the seams facing at you. You're going to pin the seams to the shoulder seams of the shirt, making sure the back collar strip is on the side of the back of the shirt, and the front collar is to the front. When you pin these together, you're going to match the right side of the collar material to the right side of the shirt.
When you're pinning the collar to the shirt, you're going to want to pin a lot more than just the shoulder seams. I suggest pinning the middle of the front of the shirt to the middle of the collar piece, and the same for the back. If the collar material is shorter than the neckline, as you sew, stretch the two to fit.
When you've sewed them together you'll have something like this:
You're then going to fold the collar material over in half, and match the seams up:
And sew them together, just resewing over the lines you made with the first go around:
And when you're done you'll have something like this!
You can do that with sleeves, with the bottom of your shirts, anything! I apologize for my poor explanations, but I was hoping that some of the pictures would make them more clear.
I HOPE THIS HELPS SOME!