I've read that I should bold, italics, heading tags, etc for my keywords. Also, that I should make sure I do this in the first few words on my site, the last few words, and repeated throughout. Does this really help to improve my ranking?
It is important to determine the focus of each page of your site, and therefore decide on 3 - 5 key phrases related to that focus. Having determined your keywords and phrases for the page, they really should appear in the title of the page, and the meta description. The aim here is to offer an insight to the content to be found on the page. Having done this, the visible content of the page will include these words and phrases as you discuss the focus of the page.
I wouldn't worry to much about the placement of these words in the first/last paragraphs, etc. What would be better is to think about writing a quality content page. A good format, where it's appropriate, is probably not dissimilar to what you learned at school:-
- Tell them what your going to tell them
- Tell them
- Tell them what you told them
When breaking up the content in this way, it's also a good idea to use headings to introduce each section of content. If you do this, and it seems reasonable to use your keywords in the headings, and in the content sections, then by the end of the page you will have written a high quality piece of copy for your page. This copy will likely also be highly optimised, quite naturally.
Try not to get bogged down with ideas of keyword density formulas, or keyword weighting. You should write content for your users, whilst at the same time remembering that if you follow some very simple rules, your page will likely rank highly because you've also catered for the search engines.