Sometimes I just close my eyes and have them walk around.
What is your character's leading center? As in, when they walk, do they lead with their head? Their chest? Are they slumped over? Squinting into the sun, looking around at their environment, or trying to avoid eye contact? Do they move with a purpose, or do they wander aimlessly?
Once your character starts walking, you'll probably start to envision their environment. If you've already chosen a setting, which particular details about it do they notice? What a character sees is EVERYTHING. (By the way, if you have NOT chosen a setting, it's a perfect time to throw them outside, have them walk past other people, buildings, nature, whatever, and imagine how they'd respond.)
I like to get my character moving, and then see if I can glean anything about the character's personality and mood by imagining how they'd perceive obvious things, like the weather. Or the greenery. Do they see bare trees as barren, colorless and dead, or do they delight in the crunch of the leaves that have fallen off of them? Does he choke on the wind blowing in his face and get annoyed that it's drying out his contacts, or is she relieved to feel a breeze against her cheeks, especially with that heavy sweatshirt crowding her neck? (And as you can see, other details about their clothes, their hair, even whether or not they wear contacts and stuff like that, will follow.)