First, what NOT to include:
- You've been writing since kindergarten.
- Your Mom (best friend, Grandma, class) thinks you're the cat's meow!
- Elementary, Middle School, High School, college credits (paper, yearbook, etc). If you were published in recognized magazines during that time, then, yes, include it.
What to include:
- If you've been previously published: where, when, what, etc; magazines are a great way to break into the writing world. Several published articles (especially in the genre you're querying) will look impressive.
- Groups you are a part of (RWA, PNWA, SBCI) (but you don't need to mention if you attend conferences regularly, but there are ways around it; say, if you met a great contact such as a writing mentor, famous author that is now your friend, or an editor requested your material, then slide in the conference--but really, it's just padding)
- critique groups
- classes you've attended (if you've studied with, say, Donald Maas)
- if you have a mentor who's been recently published and well recognized (not someone who has been independently published and no one has heard of her).
- Degrees (MFAs, masters, graduate school)
- if you're a teacher or librarian or have taught classes specific to your genre
- if you have a high traffic blog or contribute to a high traffic blog well known in your genre
And yes, your bio will be different in your query than a full author bio, especially if you have a lot of credits. If you do have a lot of credits, give us the highlights, then go into detail in the full author bio. If you have few credits (try to fix that) then your query bio and full bio might look the same. Some people like adding cutsie stuff like you'd see on the back flap of a hard back--but that's really not necessary. I want the hard facts.
Update in response to question: It's not necessary to have an author bio. I like concentrating only on the query. But make sure to read an agent's preferences first, if they specify at all. Some say to include it, if they don't, then it's up to you. If you have something impressive that will get you requests, then include it, otherwise don't worry about it.