Trying to grow back bald spots is always a problem area. Called Androgenic Alopecia in medical terms, it tends to affect men a lot more than women. Keep in mind that everyone is physiologically different, and not every method will work 100%. However, a few tips that could aid the process:
Rub your fingers all around your scalp giving yourself a nice, stimulating head massage. Use deep circular motions and get the blood in your scalp really well circulated. This activates hair follicles vital to the growth of hair, delivering oxygen to them. You can do that exact same thing, but with a prong-style hair brush or even a head massager. You might also want to re-look at the food you eat. Make sure its protein heavy. Eat a lot of lean meat, poultry, fish, beans, eggs, nuts, yoghurts and dairy.
The use of chemical substances is also another way of re-growing bald spots. You can use Finasteride, which counteracts the effects of androgenic hormones which lead to hair loss. A well-known treatment is Minoxidil, commonly known as Rogaine. It causes the blood vessels on your scalp to open wider, enabling a better flow, and thus more nourishment to hair follicles and scalp area, aiding hair re-growth. This treatment has to be continued on a regular basis. You can also opt for hair transplantation sessions at speciality clinics, though this choice might be the more expensive one to make.
If nothing works, you might consider shaving everything off, though not all women are too pleased with this option.