A whole new closet full of clothes that I like, that fit and look amazing on me. I'll get back to you on that topic. Any suggestions?
I have ugly t-shirts. I look dreadful in a crew neck and yet I get these shirts at events that I want to wear for various reasons. So I wanted to find a way to redo the neck easily (who wants to spend more time than the shirt is worth?). It also happens that they are always too long for me. New neck and hem please.
Side bar: Nothing takes an outfit down faster than sleeves or hems that drag. Frumpy. Very frumpy.
So happily the 2 alterations go together. First cut off the hem. The nicely pressed folded edge will come in handy.
Now find a neckline you like on some other garment or pattern. Trace it onto paper so you can make other adjustments and make notes about what works. A curved ruler should always be close at hand to smooth curves. Trace both front and back, people!
Really all that is required is a nice line that doesn't take off too much. The neckline patterns need to include about 1 cm seam allowance. Just recognize that the opening will end up 1 cm deeper and wider than you cut. Trace the pattern pieces onto your t-shirt. Make sure the back and front pattern pieces align at the shoulder edges and that they are centred. Cut away the old neckline. Deep breath. It's only a shirt!
Trim the hem fold you cut off to 1/2". You can adjust this amount as you see fit. I was looking for 1/4" edge showing when the neckline was completed.
Pin that folded, trimmed edge to the right side of the cut neckline. The fold faces the garment - raw edges together. 
Sew the edge to the neckline with a tiny zigzag stitch at about 1/4" seam allowance. Don't use a 1/4" foot as you make zigzag your way to a broken needle and/or foot. (Yes, done that.) Give the edging a bit of a pull to make it lie smoothly when done. My fabric was quite stable so a slight pull was all it needed. More stretch, more pull required.
I started at the back and used this You Tube video to make a mitred join when I got back to the beginning. I have tape on the deck of my machine that lines up with the needle. I use it to guide the bottom edge in a straight line when I'm doing bias or triangle seams. If you look closely you can see the bottom fabric corner is following the tape line. Here we are - all done step one!
Turn the new neck edge to the inside and topstitch it in place from the right side. Use a stretchy stitch. A plain tiny zigzag will do, but I went with a decorative stitch. Again, the fabric was stable enough that I didn't need a stabilizer underneath. I was living on the edge! Then remember to zip up a new hem. I used the same decorative stitch. So match/matchy!
