Plan your schedule. This is especially important if you have a lot of diverse activities (like WdC Birthday Week) rather than one overall activity (like NaNoWriMo). Before you even jump in, take some time to sit down, review all the activities, and plan your time accordingly. Make a note of important deadlines, prompts, word limits, and other details that will help you look objectively at your "to do" list and prioritize. Even if you're jumping into this halfway through the first week of September and realizing some activities are already going on, don't rush into things without scheduling your time so that you're not running around in a panic trying to remember everything on the fly.

Give yourself downtime afterward. When the big push is over, make sure you take some time to recuperate. There's a good chance you'll have burned through a lot of your energy, creativity, etc. and you don't want to make the mistake of diving right into another big project or another period of intense writing without giving yourself a chance to recover. And by recover, I mean still working... but working less. I've made the mistake of stopping cold turkey after an exhausting birthday week or NaNoWriMo and it's hard to get back on the tracks after you've completely derailed your motivation. Instead, set manageable goals for yourself while you recover. Kind of like an athlete will have less strenuous workout days than others to give their bodies a chance to recover, you should do the same with your writing. If you regularly write 2,000 words a day and you've been pushing yourself to do twice that number to keep up with everything during the birthday celebration, consider cutting back to 500 or 1,000 words a day for a week or two and enjoy the slower pace. Similarly, if you regularly do 5-10 reviews a week and you suddenly do 100 this week for various activities, give yourself permission to maybe only do 1-2 a week for a couple weeks until you've built your energy back up again.

Work on different types of activities. If you're really determined to get involved in the birthday week activities, try limiting yourself to only one or two of the same type of activity: reading/reviewing, writing, and fundraising. It can be incredibly stressful to have to maintain bids in six different actions, or have to do twenty reviews a day to keep up with four different review activities, or have to write three stories a day to keep up with various writing deadlines. I'd suggest going through the list of activities and picking out your absolute favorite in each area. Then, once you've committed to that, if you find yourself with more time to do a particular type of activity, start adding them one at a time. Maybe one writing contest only has a deadline at the end of the week and you decide to pick up a daily writing challenge in the interim. Or maybe one review activity only requires a couple of reviews so you feel comfortable picking up another review activity without overloading yourself.