Question: How can you try to not make your writing seem rushed?Answer:
Revise, revise, revise.
Set your work aside for a time (a day, a week, a month), then come back and revise it again with fresh eyes. Show it to other people and listen to their responses. Then revise again.
Keep asking yourself, "How can I say this more clearly, more specifically, more simply, more effectively, more passionately?" And, of course, make sure your spelling, grammar, and formatting are correct.
Sadly, there are no shortcuts. Like river water flowing over stones and turning them smooth, polished writing takes time and reflection.
Of course, some outlets, such as blogs, demand less polish than, for instance, literary fiction. And sometimes you have to write very quickly (e.g. when writing for newspapers). But in those media the writing often seems very rushed.