You don't have to rely on a tailor or keep letting your pants drag on the floor. This step-by-step guide from a professional tailor and alteration specialist teaches you how to hem your own dress pants for the perfect length.
You might not even need a sewing machine, Danni Trester writes on the ManMade blog, although you should have tailor's chalk. The tutorial doesn't mention it, but you should first know how your pants should fit.
Then, proceed with the 17 steps in the instructions, which are very detailed with helpful photos.