Most 'droopy eyes' are actually droopy eyebrows due to injection of the horizontal forehead lines (as stated by Dr. Cohen). If this is the cause the droop should improve by gently lifting up the brows. You can try to improve this type of droop by adding more Botox into the brow depressors (the frown lines) and by avoiding as much being put into the forehead lines.
If the eyelid still appears to be partially closed over the eyeball, then it is true ptosis and the iopidine (aka apraclonidine) drops can help till the Botox wears off.
Web reference: http://seattleface.com