Ernest Hemingway had this advice on how to practice to be a good writer when you're not actually at your desk writing:
You should be able to go into a room and when you come out know everything that you saw there and not only that. If that room gave you any feeling you should know exactly what it was that gave you that feeling. Try that for practice.
When you’re in town, stand outside the theater and see how the people differ in the way they get out of taxis or motor cars. There are a thousand ways to practice.
And always think of other people."
I like to do something similar, using glimpses. Apart from the people we work with or live with, we catch only glimpses of the lives others. Use that glimpse to imagine what is going on in their lives at the moment--and figure out what was about them that led you in that direction.
Was it what they wore?
The expression on their face?
Their body language?
The way they moved?
These also are the kinds of clues you can give your readers about what your characters are like, without spelling it out.
(You can get writing advice from the best writers of all time in the book, Your Creative Writing Masterclass, published by Pearson and available from Amazon or your other favorite bookseller.)