Keywords found within the first 300-400 words of an article generally reflect the bulk of keyword returns.

Use of a keyword in a HEADER (h1, h2, h3, etc.) counts for extrac credit as these are 'top-level elements' in SEO. A 'header' should summarize the paragraph(s) that follow (again, this adheres to better SEO) so don't just throw-in random headers whose summary is not detailed in the paragraph(s) that follow.

The keywords should be in the title, in a keywords section and throughout the article. It is good to have a 4 to 7 percent keyword density within the article. This means that your keywords should make up that percentage of the article. Besides that, they can go in the HTML, but that can depend on the type of format your page is using.

As Laurie stated, the title must contain your #1 keyword. Use it in the first sentence and the last sentence. Sprinkle it in the body of your work - all total use keyword(s) about 1 time per 100 words.

I don't have the sites in memory, but plug in "Free keyword checker" or something to that effect. Copy and paste your article there. It will find your keyword density. Most people I write for want a 1-2% keyword density after the Google Panda thing. Best to use your judgment and don't force keywords where they do not sound natural. Hope this clarifies for you.

You should make sure that your keywords are in the title of your article and also in the article description.  When writing articles for factoidz you will also find a box for you to specifically identify your keywords.  Try to put in keywords that you think people will be looking for.  It can also help to break up an article into sections with sub headings and using your keywords in there will help.  Also, your keywords should be used throughout the article.  You need to be careful to balance repeating your keywords with ensuring that your article is still well written, interesting and informative.  I hope this helps.

You can spread the keywords throughout your article. For example, place the title of your article in each of the five paragraphs. Avoid using the title too many times within the article. In 400-500 word articles, use the title about 6-10 times. Also, when you are writing, if you write good content, your articles will get hits almost every day. Put information in your articles that you think the reader will type into a search engine box. Write "How To" articles because people use the Internet to learn how to do things. Make sure your readers are able to accomplish the task when they read your articles. Keep writing and you will make progress.

Put the keyword in the first paragraph at least once or may be twice. Secondly, also put it in the last paragraph. Scatter few in the body, but make sure that it is below 2% in the whole article, for effective article marketing.