A few people have asked me about my alterations from bootcut to skinny jeans. I have done this with several of my pants and love them a million billion times better post-alteration. You will too. This is not only limited to bootcut...if you have some full on 70's flares, you can also use this tutorial to save them.
Step 1: try on your pants and with a pin or a piece of fabric chalk, mark on one leg where you want to start tapering (around the knee, usually), and another mark to show how skinny you want to go at the ankle. [having a cute assistant is optional]:
Step 2: with your starting and stopping points marked, carefully (if you're using pins) remove the pants and turn the pants inside out, moving your pins to the inside. Don't worry if your markings move a centimeter or two...these are rough measurements and can be adjusted as we move on.
Step 3: Then with your pants turned inside out, sew from the knee pin to the ankle pin at a nice even angle. Start sewing just barely off of the pants and gradually angle onto the pants. This will make a nice taper with no weird tucks or gathers at the knee. [as you can see, my pants are not turned inside out here, but make sure yours are! Also, make sure you do this seam on the inside of the leg. The outside will be much more noticeable!]:
Step 4: try the pants back on with one leg "skinnied" and one leg not. If you are happy with how the skinny leg looks, move on. If not, resew your seam and then try them on again. Once you're happy with your skinny leg, cut out the extra fabric and secure your cut edge with a zigzag stitch or a serged seam.
Step 5: fold your pants in half and measure the skinny leg against the bootcut leg. Mark where you started and stopped and then do an identical seam on the other leg. Try your pants on and make sure you're happy with both sides. If you are, cut out the extra fabric on the second leg and secure the raw edge.
And Voila! Skinny Jeans!
A quick note: These jeans were a little bit long, so I considered hemming them, but then once they were done I decided I liked the bunching at the ankle. Plus, I figured I'd be cuffing them occasionally so I wanted to keep the nice professional hem at the bottom that would show when cuffed. If your jeans are super long and must be hemmed, I'd suggest using Melissa's excellent tutorial here.