Attaching Cuffs And Collar Stands

I don't see this method mentioned much online, which is strange.  Most patterns neglect to mention this method also, but most patterns use very archaic (and frustrating!) techniques.  Cuffs and collars are something I always see on forums that people have difficulty with, and this method makes it so easy you'll want to sew a million shirts.  This is the way all the manufacturers do it, so take pride in learning to sew at a sweatshop level.
This all starts when you are making the cuffs and collar stand pieces.  Before you sew them together, take one piece and press a fold towards the wrong side on it in the amount of the seam allowance.  I fold and press just one side, as pictured.  On the collar stand, it's a good idea to sew this fold down, as the fold has some curvature to it that makes it difficult to stay put and work with.

From here, sew and turn the pieces as normal and press.  Do the same for the collar stand, which is a little tricky because it has curves.  Note, if you're doing a cuff/collar stand which has a different fabric on the inside than on the outside, you want to put the fold on the piece that will be on the inside of the finished garment.  In other worlds, put the fold on the piece that you don't want others to see.  
When you are ready to attach the pieces, here's where the ease of this method shines through.  Pin the unfolded side onto the right side (the outside, or side that will be seen) of the sleeve or neckline, with raw edges both on the same edge.  See the picture, this is the collar stand attached to the neckline of the shirt.

This is the 'outside' part of the garment, the part people will see.  If your sleeve/neckline has a different seam allowance than the cuff/collar stand, than pin it so the folded edge is as close to the seam allowance as possible.  Now sew as close to the fold as you can, making sure you don't grab it by mistake.
Now, turn the cuff/collar up, and stuff the raw edges inside, as pictured.

Well, not really stuff, because the beauty of this method is that it pretty much just flows inside when you fold it.  From there, top stitch, making sure it grabs the underlying layer.  Look at this, here is a cuff after being sewn on and flip up:

See that basted line just above the fold?  That is the fold on the other side of the garment.  You want the fold on this side to be on that as close as possible.  That way, you can be sure you are sewing through both layers and that they are level on both sides.  This is very difficult, believe me, and takes a lot of practice and finagling with the fabric.
This is why it's so important to stitch close to that fold, because if you don't, it will make it difficult to top stitch without things getting weird on the right side.  You'll also see how crucial it is, especially on the collar stand, that the fold follows the raw edges on the other piece exactly.  If it doesn't, it's impossible to top stitch the underlying piece and have it hit the top layer.  Follow that with adding whatever other top stitching you want, such as outlining the sleeve, bar tacking the corners for strength, embroidering dragons, etc.
Now, lets say you are doing a design where the inside piece of the cuff/collar stand is a different fabric than the outside piece.  And somewhere along the line you got all confused and folded the wrong piece.  Believe me, been there, done that, but luckily there's a fool proof version of the technique here, one that I have to use very often.  I call it Easy Mode, and it's the best way if you're a beginner and you cuts and measurements aren't that accurate yet.  The big difference is instead of pinning right side to right side, you will pin right side to wrong side.  Pin the RIGHT SIDE of your cuff/collar stand to the WRONG SIDE of your sleeve/neck.  In other words, pin it to the inside of the sleeve/neck.  Now, instead of doing finishing stitches to attach it, just baste it.  Flip it and top stitch it making sure at least one top stitch goes through both layers.  Now pull out the basting, and no ones the wiser.  Your secret's safe with me.  I do this method more than the real way it seems... 
Also, on this method, refer to the last picture above.  Remember how I said you want to get the fold on top of that line of stitching as close as possible?  Well, when you do this method, you don't have to worry about being that exact.  As long as you are below that line of stitching (not too far, though), you are guaranteed to sew through both layers.  Makes it easy-squeezy to get a perfect top stitch on the outside of your garment, which others will see.
The other way of doing cuffs and collar stands, that I see most patterns still use, is sort of similar.  Back when I had you only fold one side, you can fold both sides instead.  Then it's a matter of stuffing the sleeve/neck into the cuff/collar stand.  Some prefer this method because it's easier to see that both layer are folded the exact same way, so that you can more easily top stitch it evenly.  Try out both and see what works for you!   
-Cat

White fabric is 100% Organic Cotton from Michael Levine in Downtown Los Angeles, also available online here.  This is my go to fabric for white.  It's incredibly soft, and has a very similar texture and sheer to Oxford.  Not too thin, yet very light.