I admire New York Times war reporter David Finkel, whose "The Good Soldiers" (link is to my 2009 book review) may be the best book about war published in the new millenium. Finkel is famous for his focus on details, and "The Good Soldier" takes readers inside the heads and hearts of American soldiers in Iraq as they struggle to both survive and figure out their complex mission. Finkel spent 18 months living with these soldiers, many of them still teenagers, going out on patrol, talking to them at night after difficult, nerve-wracking days, listening to them in hospitals after they'd been wounded, and paying attention to every detail he could absorb.
Any writer who wants to understand the importance of observation should read Finkel, who's a master at finding the small details that reveal larger truths. "The Good Soldiers" is heart-breaking because it meticulously describes the day-to-day toll of war on young men.
So write with your senses in mind. Walk around and take everything in, listen, smell the air, pay attention with all your senses, and find meaning in the details. When I worked as a reporter, I used to show up to events an hour early and see the organizers setting up. Many times, I'd get my best material from speaking with organizers during these quiet moments before the event began. If I'd shown up ten minutes before, nobody would have talked to me. I used to stand quietly in the back of the room and watch and listen -- that's a great way to learn.
Listening may seem simple, but it's not. It's every writer's best tool. When I was reporting on a story, I used to prepare 7-10 questions in advance. But I was always ready to listen and follow up with more questions when I discovered something promising, something that would grab my reader's attention. It helps if the writer/reporter has a general idea of what he is looking for, but it helps more to allow for serendipity, the surprising moments that bring a story to life. Good luck happens, most of the time, when you keep your mouth closed and pay attention to what's in front of you.
In terms of the actual writing process, you may want to alternate from concrete details to the abstract or reflective. The details you include tell readers "this is what I saw," while the reflective/abstract tells readers "this is what meaning I found in what I experienced." Take in the world through your senses, then reflect upon what it means. Yes, this will take time, but sensing and reflecting must precede all good writing. If you're not sensing things around you, you certainly won't write well. The more you use your senses to filter the world, the better your writing will be.