Well, of course, has to do raiding, on the level of progression that I myself am at that moment in time. This is obvious, since I love to raid. It does not necessarily have to be a progression guild, but will not hurt. I have so much experience with casual guilds and watching them struggle with putting good raids together.
But the two most defining elements of any guild, in my opinion, are the guild leader and the raid leader, in my mind, two distinct people. These are two guild members who have the most impact into the nature and success of a guild. They set the tone and atmosphere in their respected repartments and are responsible for the most essential functions. Usually, the raid leader is also the guild's main tank, though this is not always the case.
I believe in a guild with a clear vision of what it wants to do and the guild's leader should embody this aspect. He should know exactly how many and what kind of members are apart of the guild, with a healthy firmness of rules. Does not mean rules have to be absolute or so strict you choke on them, but make sure everybody follows them and no one should get preferential treatment.
For the raid leader, the responsibility is to schedule and make sure the raids run smoothly. Same rules apply, to make sure bad apples are weeded out and everyone comes both prepared and follows the set rules. If either of the above mentioned, is a bastard, unqualified or unable to follow (or even set proper rules), it quickly reflects on the guild's performance and will eventually break it apart.
One huge mistake I see many new guilds do, particularly casual guilds that are based largely around close-friends, is at the beginning, reward seniorship by making their friends officers, as somehow as a sign of prestige or priviledge. I have seen it so many times and it is never anything but a recipe for disaster. This might work when the guild only has 15 members, but once they push to 30 and 40, it ends up with 10 arrogant officers who do nothing to contribute to their position as leaders, but simply reap the benefits, often getting priority on raid spots, what they are allowed from the guild vault, and distributed loot.
"There are no bad crews, only bad leaders."
Essentially, the guild simply continues to revolve around the senior members, with the rest viewed mainly as a space holding force to fill the gaps for 25-man raids, and worse, have no voice at all in anything that the guild does. Understandibly, the leadership makes the final calls, but it is the most common and obvious sign of a bad leader, if they are incapable of taking input from other members without referring to their status for confirmation about their qualifications.
For me, I don't see how a guild ever needs more than a couple of officers. Even a guild doing 25-man raids, only need a 2-3. If it is a particularly large guild, signing officers for various subgroups, tank, dps, and healers is appropriate. But still it is no sign that they are more "important" than anyone else. They simply are there to manage their departments.
If you now find yourself thinking to yourself that as an officer, of course you deserve more than non-officers, think about this; without those "lesser beings" you would be managing empty air, you would not have full raid groups, and if you truly and honestly feel you you deserve better rewards then they, does that sound like you're thinking about the guild's best interest, or your personal greed?
Because so far, I have not found evidence of a single guild that succeeded in good progression by only looking after a select elite and leaving others behind. The more division in gear and skill there is between members of a guild, the worse the it will do on the long run.