Now is one of the best times of the year to people watch.
If you are struggling with ideas for characters (or characteristics), go hang out at a mall near the food court or a busy section where a lot of foot traffic is passing through.
Guaranteed, you will see people from every walk of life.
Leave the binoculars at home, but take a notepad or laptop and jot down some notes as you watch people. Observe how they dress, how they walk, how they interact with those around them. Are they smiling? Grumpy? What about them drew your attention? Try to capture information about a variety of people.
Make lots of notes, as detailed as possible.
Down the road, if you find yourself struggling with a character, pull out those notes. There is sure to be something that will spark your creativity and get you back on track.