First, justification for my subjective whatnot: I’ve been running competitively to various degrees since middle school and am currently in my late 20s. I’m currently running 15-20 miles weekly. That said, “running style” is super-subjective and ultimately you have to decide what works for you personally.
I took a year or so off post-college and had to get back into it. Like you, I found I had somewhat “forgotten” how to run. Mostly I think it was a case of various supporting muscle groups atrophying enough to make the act of running seem less-than-natural.
Anyway, the thing about running is that there are really two schools of thought: those who feel that we run the way our bodies are built (our “natural form”) and those who feel there are biomechanically correct principles that can be learned and applied by everyone. While there are great runners in both camps, I fall in the latter and I suspect that the great runners in the first group got lucky in that their natural style just happened to be the “good one” that the rest of us schlubs have to learn by trial and error.
That said, I’m going to have to completely contradict Trunk (sorry!
) and say that you don’t want to be a “heel-striker” as this phenomena is usually associated “over-striding” (thrusting your leg too far ahead of your body) and frequently leads to knee and shin injuries if you’re putting on a lot of miles.
Some things I like to keep in mind while running:[ul][li]Land on the ball of your foot. Heel-striking tends to encourage bad form and leads to injury.[]Focus on picking up the foot that is on the ground. Don’t worry about the foot that is in the air-- it’ll find its way back to earth. The less you think about foot in the air, the less you’ll tend to beat it into the ground.[]Never straighten your knee. It is stressful to the joint and, once again, encourages bad form.[]Try to keep the foot that is on the ground there for as short a time as you can while striding comfortably. In general, the faster the runner, the less time their foot spends on the ground during one “stride”. Watch full motion video of a competitive runner or just go to the local 5k “fun run” and watch the lead group after about the first quarter mile. (the initial sprint is not a good place to learn about form unless you’re interested in sprinting form)[]Lean forward slightly, almost to the point you feel like you might fall-forwards.[]Keep your shoulders and arms relaxed[]Most importantly, stretch before and after you run. …and start slow! I know, the temptation is to run just as hard as you did before you took some time off-- but you can’t and you’ll hurt yourself if you try.[/ul][/li]
[QUOTE=Trunk]
However, the guy in purple behind the tall thin guy looks like he’s about the land on the ball/flat of his foot.
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IMHO, there are only two guys in that picture who look like they might have decent form: #3846 (the guy in blue) and the guy in the far-left foreground wearing red (we can only see the back half of him). It’s hard to tell from a still, but both seem to have their knees-bent and are on the ball of their foot with a slight forward lean.
…just my two cents. 
(OK, I guess it was more like a buck-fifty. Sorry for dragging-on.)