Since I had to re-hem a suit some years ago, I took apart a more fancy hem on the pants and developed my own technique. Ironing is crucial. I set the iron on its maximum temperature, since I'm setting creases rather than merely taking out wrinkles. Depending on the fabric, this requires some caution so that the fabric isn't damaged. Since I prefer wool over other materials, this is rarely a problem, but wool-synthetic blends require a more light touch with the iron to set a crease.
Here is now what I usually do...
My inseam is 25", so everything is referenced off of that. I start by cutting the pants to somewhere between 28 1/2" and 29" (inseam plus 4").
Then I fold this in to 28" (inseam plus 3") and iron. (I don't turn the pants inside-out, so the picture below is of the outside of the pants along the inseam. The extra fabric you see from 28" to 28 1/4" is the inside of the other side of the same pant leg.)
I machine stitch this edge. Thread color does not matter, since it will be hidden.
I bury the bitter ends of the thread on the inside of the seam, so they can't catch on anything.
Then I iron another crease, now at 26" (inseam plus 1").
And before any further stitching, I fold and iron at 25" (the final inseam). This almost always requires several passes of the iron since there are many layers of fabric to crease.
At this point, the hem needs to be anchored with a stitch. But since I don't want the thread to show through the outer layer, I don't stitch this with the machine. So I hand stitch through all layers but the outer layer.
Here is the view from the inside of the pants...
... you can see no thread on the outside ...
... the stitching holds together here.
Here is the finished product.