I usually have the opposite problem of hemming and have to lengthen my pants, but that still involves the same steps. To start, try on your pants and have someone pin them up where you need to have the hem end. Take them off and finish pinning around, then iron in the hem to ensure it's straight.
Next comes the sewing. I have a Brother Sewing Machine so my settings will be different than another model. However, all hemming will require a specific foot attachment and setting your machine on the blind stitch hem. Below is a video of how to switch the foot attachment as this was a bit confusing for me at first.
Once you've changed feet, ensure your machine is set to the blind stitch hem (for me it was 11). Then turn your pants inside out and fold the edges over with a small piece of the bottom sticking out (see photo below). You will then place your pants with the folded edge to the left and the open edge to the right of the split on your foot.
Your sewing machine will now do the rest for you! The blind stitch hem ensures you cannot see a stitch line on the exterior of the pants. And voila - hemmed pants at a fraction of the cost of a tailor. Total savings on 20 pairs of pants per year: $12 x 20 = $240. You could afford to buy a sewing machine with those savings!
However, if you don't like to sew/don't know how, there's another easy solution for hemming. Stitch Witchery is a no sew adhesive that you simply apply and iron on to hem your pants. How easy is that? And for $3.77 you can save $236 a year on tailoring.