Your ability to grow a full and thick beard is almost entirely a matter of genetics. If you have insufficient hormone levels, which determine the growth of facial hair follicles, you may not be able to grow the beard you want. However, this doesn't mean you can't attempt to grow a beard. On the contrary, you have plenty of weapons at your disposal to make your spotty beard appear thicker. Employ a little grooming trickery to grow your beard out longer, but create the appearance of a short, full beard.
Grow your beard out until bald patches are no longer visible. Do not trim your beard during the growth period. You need as much length as possible to cover your problem areas.
Apply pomade to your beard. Use just enough pomade to give you control over the direction of your whiskers.
Brush your beard in a downward fashion with a soft bristle brush. Brushing your beard makes it appear uniform across your face and helps wrangle in unruly whiskers.
Trim long, unruly whiskers with scissors, then brush your beard again.
Consult your doctor if you have any concerns that your sparse beard results from a hormonal problem.