加强 (jiāqiáng) is primarily used in formal or semi-formal situations. It sounds serious and purposeful. You wouldn't typically use it to say you're “strengthening” your friendship while chatting casually with a friend (you might use `巩固 gǒnggù` or just talk about hanging out more).
This is the most common context. It's used to announce new policies or focus areas.
It's standard vocabulary in the workplace for discussing strategy and operations.
It's used to talk about improving one's skills or knowledge in a structured way.