Sensory language is a powerful tool. How are you using all the senses? What can you smell, taste, see, hear, touch?
What time is it? Daytime? Nighttime? Are you in an urban setting where the streetlamps have all turned on at night? Are you in the countryside where you can see all the morning dew glittering at sunrise?
Are there other people in the area? If so, what are they doing? Is there traffic? Is there animal or plant life?
Are you indoors? How well-lit is it? What's the personality of the dรฉcor? What's the view outside the window?
When your character takes actions, they are engaging with the world described above. You don't have to describe the answer to every question, but knowing it can help inform your writing with anchoring details. You can actually set the 'scene' in as few as two sentences to get an image across. You can do a lot with a little!
A helpful method I've found for writing in-depth descriptions -- such as people, rooms, or objects, or clothing -- is to begin with a broad description, then zoom in with details. So in a room, for example, I might start with a broad descriptor ("It was a quaint little living room.") then describing the way it looks in a more detailed way ("A patched, faded couch sat beneath the light of an open window, while beside it sat a wooden bookshelf filled to bursting with well-thumbed novels.").
Reading helps, as mentioned above. I've actually found poetry very inspirational from a descriptive-writing perspective, as well as reading screenplays, which have to describe settings and costumes in great detail.
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