From the top four things to see.....the Kennedy tomb is within five minutes walking from the visitor center. I was expecting something huge and grand....and it's a bit more simple than that.
From the Kennedy site, it's a good ten minute walk over to the Tomb of the Unknown. It is a hilly walk, so don't think this will be a easy walk.
From the Tomb of the Unknown....it's a good ten minute walk over to the Arlington House. For months, I've been noticing it from the Pentagon. I kept thinking this Arlington House was huge, but once you climb to the top of the hill....it's really a fairly small house with a grand entrance.
Then, you've got this fifteen minute march out to the far extreme northeast corner of the cemetery. In fact, you reach a point where there's a gate, and you have to exit the grounds, and then about 500 feet away, is the Iwo Jima Memorial. It is huge and highly impressive.
My advice? There's no sodas, ice cream or anything that you can buy at the cemetery. Bring a bottle of water with you. If you tire easily on hilly walking....this may become a problem and you ought to use the bus service. I spent the morning walking and got fairly exhausted after two hours there.
There are a number of odd things about the cemetery. There are wives buried there. There are kids buried there. If you can find the steep incline where the Thresher crew are buried...it's just headstones and nothing else (they were never found).
If you wanted to make a day out of this, then start here in the morning (arriving by METRO), then leave and cross the Key Bridge (less than 500 feet from the Visitor Center. It's a 10 minute walk over the bridge and you then arrive at the Lincoln Memorial. You can hit both it, the cemetery, and the WW II memorial in one day before you call it quits. The Smithsonian METRO station is about a twenty minute walk from the Washington Monument, which is just across the street from the WW II point.
If you aren't up for walking four miles in a day...then don't do it. Rely on the bus tour business and make it simple.