The Basics:

Strengths and Weaknesses

An important part of playing any comp is that you understand the strengths and weaknesses of it before you even queue for a match. In the case of WMD the strengths and weaknesses are as follows:

Strengths: strong cc, hots, MS, gib potential, unsheepable healer
Weaknesses: no dispel, warrior can be gibbed, very susceptible to drain

Because your team has no dispel, it's very key to have excellent communication and keep a solid CC rotation up at all times. This means swapping from sheep to cyclone or vise versa to keep multiple targets locked down at a time.

Play Style

Because of the nature of this comp, you have to go into every game preparing to be focused 75% on being defensive. Warriors can be gibbed easily, as can druids if you and your warrior are focusing on getting a kill rather than assisting your druid. Overall each player needs to always have it in the back of their head to be helping out other players that are being taken down. In this comp it is much much more important to keep your players alive than it is to get a kill on the other team. Your team has relatively few damage cooldowns (WE). If the mage can manage to save his pet until mid or late game you can outlast the other team's cooldowns and then go for a gib with a good cyclone and sheep rotation on the healer.

The Mediums

Waiting out the DRs

Because of majority of this comp circles around CC and your inability to dispel CC you have to coordinate when to make your gib. Often times a team will CC your warrior because he's generally the largest immediate threat. During this time the mage and druid should also be CCing their offensive targets. As soon as your warrior is on the 3rd DR or immune your team can plan to kill a target. Since you haven't CC'd the healer yet you can now get full sheeps, cyclones, a bash, a feral charge, an intercept, a pummel, and a CS on their healer. (Yes, we've done a lock-out as long as that) As you can see from that list, if you plan it right, you can completely shutdown a healer. At the same time you need to be careful that you aren't wasting your DRs on damage that wasn't a threat to your teammates dying.

Communication

Yes, I said it, we use ventrilo for a reason. Communication is key key key to this comp working. Without a solid CC rotation this comp will fall apart and you'll watch your druid desperately try to hot through 3 people slamming your warriors face into the ground while you get tonguesd, feared, then deathcoiled into a spell lock. Use NECB, watch when cyclone ends and start casting your sheep 1.5 seconds before it does, have your druid do the same for your target. Also, pre-call everything you do. That means say "I'm CSing next heal." instead of "I CS'd the heal." as IMMUNE comes up on your screen because the druid cycloned at the same time.

Call if you're trying to get a drink. Call where you are, call los, call what you're casting on, whatever, call something. If vent is silent then your team isn't talking enough.

The Conclusion

The most important aspect of this comp is that you communicate and take advantage of situations. It's easy to say do A, B, and then C and then win, but more often than not those steps aren't going to be easy to execute. Your team needs to trust each others CC and be able to adapt to any situation with comfort. Experience will yield a lot of these aspects so the best way to improve is to play. After each game, even if you win, discuss what could of gone better and how you could of guaranteed that win, instead of barely pulling it off. Also, every one in a while check how your mana is compared to the other teams, try to remember what CDs you've used, and what CD's they have. A lot times, even if it seems bad, you may be in a good position during the game assuming you get back on your feet. A game where you are lower hp, but you have more mana and still have CDs means that once you get healed back up, you have the advantage. This comp is a lot of fun, and provides a break from the standard PMR for a mage. I really enjoy playing with the people I do, and because of that I choose to keep playing this comp.