(My is tongue is firmly in my cheek. I thought it would be fun to turn the advice that writers get on its head.)
There is a lot of information out on the web telling agents how to get a good writer. Some of it is good, and some...not so good. But as often as the topic comes up, it never gets old. Every agent wants to know how to get the writer of their dreams.
First, I know you've heard it a million times, but it's all about voice. When you're posting on your blog or on Twitter, writers are reading what you are saying. And like it or not, they are judging your voice. Be yourself, always. You want the writer to love the real you, right? After all, you will hopefully have a long relationship together, and it's important that you can work well together. So, by all means, be yourself. At the same time, don't let bad days cloud your tweets or posts. Think before you hit 'send' or 'publish'. Voice is something you can't fake, but you can make sure that you're putting your best foot forward in public areas.
Second, when you're looking at a potential relationship with a writer, don't be afraid to ask for references. Beta readers and critique partners can give you a day to day feel for how the writer responds to criticism and revision requests. I know everyone always says that the writers are the one with the power. After all they are the ones that create what you sell. But the agent/writer relationship is just that. A relationship between (at least) two people. Each bring their own strengths and resources to the table. Don't sell yourself short, or think, "I'm not worthy" when dealing with writers. They can smell fear.
Lastly, keep at it. You may not find the writer of your dreams in that first email, or even in the 500th email. The difference between success and failure is that a successful agent keeps looking. There is a perfect match for you out there. Keep faith and keep reading queries. Someday, you'll find the writer of your dreams.