1) Web site pages as long as Santa's naughty list - Don't make us page down through pages of your bio. The standard web rule is the user should not have to page down more than 2 times. I personally prefer 1. Your web site is an executive summary. You only need something short and sweet. Web sites reflect your writing. If you drone on for pages - I might not want to read your book. If you have the attitude - "Ill just get my web site up and work on it later", its the wrong one. The minute you launch it - people can see it. Keep it simple, professional, and short. Again, you can get help on Godaddy, they even have templates from which you can choose.
2) Business cards, bookmarks, and brochures from The Land of Cheapo. Come on! Nowadays you can get inexpensive, solid quality stuff from various web sites. You really don't want a white business card with your face on it. You really don't need a bookmark that is so flimsy it can be used as origami. Do yourself and your image a favor, invest in high quality pieces or don't do them at all.
3) My only target audience is children between ages of 0-18. Everyone has more than one target audience. Age is not the only way to segment your audience. There are others such as by topic, by regional as well as looking at the type of media, type of reader (library, bookstore, book club etc). Take some time to think through all of your target audiences and all the ways you can possibly reach them - you should be able to come up with at least 3 audiences and 3 mediums for each.
4) Just gonna wing it. Everyone needs a plan. Just like you need a plot for your book before you write, you need a marketing plan before you can market. Some people think that winging marketing is effective. Nope! I'm not talking about creating a 100 page word document. I am talking about a process where you - as the writer - identify your target audiences, key mediums, key timelines, key events - and set up key contacts in advance. Your materials, plans, and contacts should be in place 6 months before your book comes out. Don't wait until your book is out before you think about it.
5) I don't know computers so I cant do marketing. What? If you are selling books to kids, you need to learn computers. Nowadays at least 50% of marketing (and I am being generous, I think its more like 60-70%) is online. You need to know how to blog, how to do a basic web site, how to start a myspace or facebook page, and how to text/twitter. You also need to keep up with the youth trends (Ypulse is good for that) If you don't know how to use all these, they all are set up pretty easily to figure out. Some even have tutorials. This cannot be an excuse anymore - unless you don't want to sell anything.
Marketing and Pr are critical to your overall brand. It is better to invest in a few key pieces than to do a bunch of bad pieces. Take pride in your materials as you would take pride in your book. It is a reflection of you.
In addition to the bigger things, if you are going to deal in marketing and PR yourself, it's still important to dwell in minutiae. so be mindful of all the little things. Like copy, grammar and punctuation. These all make a different on web sites, blogs, and other marketing materials.
So get out there and market or you could always use me :)
If you have any questions, post them in a comment and I will be happy to answer. :)