OK, so what are these ensemble skill thingies? And will I get a huge, frickin' NBA contract if I have them?

No contracts, sorry. Ensemble skills are those things musicians do to play in groups.

Let's look at what ensemble skills are not:

Ensemble skills are not technical skills. That means, you don't have to be able to play a clean, consistent sound. You don't have to be able to play with blinding speed. You don't have to be able to play fast for long periods of time. You don't have to have a metronome in your head and keep rock solid time. You don't have to be able to play distinctly six different volume levels on demand.

Ensemble skills are not musical expression skills. You don't have to be able to craft musical phrases with microdynamics, be able to play leading/trailing/on top of the beat on demand, or otherwise fine tune what you're playing.

You can be a raw beginner--never have picked up a drum in your life--and practice ensemble skills from the outset. You can play your drum only at midnight under a harvest moon and practice ensemble skills. You can have played by yourself in a locked closet for a dozen years and practice ensemble skills the very first time you drag your drum out of the closet and into public.

What ensemble skills are:

Ensemble skills are those basic skills that allow groups of people to play music together and sound good. What, in real terms, does that mean?

1) The foremost ensemble skill is that of listening to other players. It moves beyond listening to enjoy the groove to listening with the intent to build the sound.
a) You listen to match the volume you're playing to the volume of the other players. If others can't hear their own playing because you're too loud, you've failed. If the dancers or listeners hear only you, instead of a blend of the whole group, you've failed. If you have a drum that is much louder than other drums in the group, you have to play extra soft, and if you can't, change drums or sit out. Your sound should blend in with everybody else's sound and create a group sound that is balanced.
b) You listen to hold tempo with the group. If you can't hold tempo very well, you listen closely to those who can and match them.
c) You listen to match the feel of what you're playing to the feel of what the group is playing. If the group is playing a very sparse arrangement of a rhythm, then filling wildly doesn't fit.

2) Understand the roles in the group and when to play which one.
a) You play the base rhythm most of the time. The base rhythm pattern is what holds the whole thing together and is the most important part of the music. The base is normally held by the dohola (bass doumbek), def, and muzhar, though darbuka players can hold it, too.
b) You understand how the lead is going to work, if you want to play lead darbuka. If a scored lead fill is being used to provide the feel of the rhythm (a specific variation on the basic rhythm), then learn it before trying to play lead. When it comes to lead soloing, you wait until your turn and then you shine as brightly as you can; if you always try to fill against the variation or when somebody else is soloing, you've failed.
c) You know what roles the different instruments you can play usually take. As noted above, the dohola, def, and muzhar usually play base, and the darbuka usually plays lead. The saghat (zils) usually provide texture, along with the riq, and the riq can also play lead.
d) Heck, simply being able to stand in on a different instrument is a valuable addition to a group! A def player who does nothing except maintain the basic accent pattern is a godsend for a group.

3) Understand that it's all about the group sound. If you're playing just for the catharsis of playing, you've failed (unless it's a nice hippy circle or Pagan circle or otherwise expressly not about the music). You are involved in creating music as part of a group and it involves caring about the sound and working to get a good sound. If you don't have much experience or technical skill, you simply find somebody who does and concentrate on matching what they do. If you can't tell if you're playing too loud, you ask somebody else if you are. If you don't know a rhythm, you find someone who's playing the base line and match what they do. If you want to try a different drum, you ask somebody who has one if you can try it (and if you've never played one before, ask if they'll show you the basic techniques).

What you don't do is bang away without regard to what others are playing and how it sounds. If the fast tempos all slow down and the slow tempos all speed up to the same moderate tempo in the end, there's a problem. If you can't hear anyone else playing, there's a problem. If noone else can hear themselves playing alongside you, there's a problem. If you constantly wail away, wildly filling, there's a problem. If the dancers ever complain that something sucks, there's a problem. If the dancers beg off of dancing because of headaches, there's a problem. If every time you play a particular rhythm it sounds like every other time you've played it, there's a problem.

These are general thoughts on the subject and may be expanded on later to provide more detail. As I've said before, I've been in some very good circles with absolute beginners. Beginners are able to match volumes, follow tempos, hold base rhythms, and trade off solo leads fairly well with minimal practice, so beginners have a place in a group the same as experienced players.

Good drum circles can always be on the agenda.