I’m in the middle of applying to a few different writing sites. Although many will take your portfolio into account, most of them give simple writing tests. The great thing about a writing test is that if you actually write well but don’t have a great deal of experience, you can get some good paying jobs. So, for those of you taking a writing test, I recommend double checking your spelling and grammar. If you’re not asked to be objective, keep the writing positive, unless it is a critique.
Other than that, keep your tone consistent and make sure to read and read again.