I've ran 2 5K's recently, and both were similar in this.

It's an easy event to get into, without any hesitation or training. Here's my $40, give me a t-shirt, timing card, take my photo, and I'm going to walk and gab...or whatever.

In both races, being up near the starting line is important. Because all those people in front of you, are going to be in your way, if you are trying to run it seriously.

In a combined 5K and 10K, I spent the first Km trying to get around all the people that started before me and were planning on going slow, walking, etc, and spent part of the time running outside the cones just to have an open lane. The 2nd Km was spent dodging the slow 10K group.. A little after that I settled into a group of 10K'ers that were running at a good clip ~7min/mile and had a good time with them. Pretty well spaced, and focused on the run. Started going so well that I went off the 5K course just following that group, and missed my turn and ran an extra block. I ended up getting back on track, and ran ~3.5 miles instead of 3.1 miles.

So for strategy.... half an hour before race start, get up on that starting line. You'll look goofy waiting there, but it's worth it.
When the race starts, run balls out and get out in front of everyone, and then keep running.