1) First, try on your jeans and the shoes you'll usually wear with them and cuff the jeans to exactly the length you'd like. Pin this cuff in place before removing the jeans. This step is a bit easier if you have a partner to help you pin.
2) Next, measure the length of the cuff including the original hem. We'll call this measurement A.
Unpin the cuff and re-pin it to measure 1/2 of measurement A excluding the original hem.
For example: if measurement A is 2 inches including the hem, your pinned cuff should measure 1 inch excluding the hem.
3) Using a thread color to match your jeans, sew this cuff in place. Use a straight stitch and stitch as close as you possibly can to the original hem.
4) Finish by pressing the cuff up out of the way inside your jeans and then tack the cuff in place by making a few stitches at both of the side seams. This will keep the cuff from drooping down and ruining the magic.
That's it! Now throw on those fancy jeans and walk tall. Add a pair of heels and no one has to know you've got a 30 inch inseam.
I'll stick with my dirty flip-flops though. Just keepin it real.