Friday's fill up fast! If possible check in midweek.
I agree with Melissa.
Fridays, I think, fill up quickly because of weekenders coming in.
Saturdays are probably popular for folks coming in longer than just the weekend.
Sundays are likely next for longer term visitors (longer than a weekend) who can't get there on Saturdays.
Finally, I also agree with lbmiller77 about arriving early in the day if possible. In
MDE you can request 1500 and an 8am arrival, for example. But let's say I am arriving the same day and requested 1500 but showed a 3pm arrival. By the luck of random assignment, my pre-assigned site is in 1500 and yours is in 2000.
At check-in when you find out you're not in 1500, you can ask again if it's possible. I've done this in the past and I believe what happens is they will grant your request and bump someone like me out of 1500 to 2000. Essentially they swap us. You are happy and I am none the wiser when I arrive. (I have done this).
The other thing that happens sometimes when you arrive early is someone is leaving that morning (and you may or may not have their site) but they haven't left yet (it's before 11am) and the site has to be cleaned and prepped before it is released for assignment. You can offer to the CM checking you in to wait a couple hours for a site to come available. In that case, they will "check you in" so that you can't be bumped but they won't tell you the site number until it has been released. Then it will come in a text after it is released and you can drive down to it. (I have done this and it was great).
No guarantee of course. One trip I did all the above and still got stuck in 2000. On the way to it I drove through 1500 and every site was full at the time. So I guess the CM's do try if possible to meet requests.
Bama Ed