If you find your legs are still too sensitive for shaving no matter what steps you take consider using a hair removal cream instead. For normal skin use a twin blade for the best results. Replace your disposable blades after every 4-5 shaves. Remember to shave in the direction of hair growth to get a clean close shave. Shave underarms last as those hairs are course and can dull your blade prematurely.
Underarm hairs grow at all angles.
Use light pressure and go over underarm area many times to remove all the hairs. Always remember to rinse your razor or shaver thoroughly and let air dry. Do not rub a wash cloth over the blades to remove debris as it can dull the blade. Apply a moisturizer or aloe gel immediately after shaving to soothe the skin and lock in moisture. Don't shave dry if you can help it.