You can be invited to join the Wiki Ninjas blog or you can ask to join it in the comments below (or email/comment to Ed directly). Either way, you'll be expected to meet some requirements.
To become an author of the Wiki Ninjas blog, you must meet the following requirements:
If you're stuck on #5 (you're not sure what your unique value can be), here are some things you can do that will almost guarantee we'll want you to join the Wiki Ninjas blog as an author:
NOTE: Microsoft employees can also become authors if TechNet Wiki is related to their job, or if they're on one of our Wiki Councils (such as the Community Council or the International Council).