There seems to be quite a bit of confusion about what does and does not work when optimising the factors on a web page, just to be totally clear about this, when we refer to on-page optimisation we are talking about changing the code on a page, usually aspects which are not seen by the average site visitor, but they help the search engines determine what a page is about.
Probably the single most important factor is the title tag, it’s essential that this has your keyword at the start, it’s a common mistake to put the company name first, however the first words carry more weight, so save the company name for the end of the tag (if at all), unless that is what you are optimising for.
Don’t fill the page with keywords, use your keywords by all means, but whatever you do, don’t use them every second word, it will look bad to the visitors and the search engines will just ignore it anyway. If you need some ideas for alternative words which would sit well on the pages have a look at the Google wonderwheel it will give you alternative, but related terms you can use on the page.
The keywords tag is virtually useless, although it’s a good place to put them, so you can easily remember which terms you are optimising a page for, I also tend to chuck in a few regional terms too, something like Swindon, Wiltshire, UK, I’m not sure why I bother, probably just force of habit I suppose.
Same with the description tag, although this can be used to encourage more clicks, as although it has no SEO benefit, it does get used for your listing on Google, so a well written description can help indirectly by increasing click throughs.
Bold an italics used to help, but I’ve not recently seen any difference in using them or not, so just use them to lay your pages out well instead and actually higlight anything which does not fit in your header tags.
Of course there are options available if you aren’t comfortable doing this type of work yourself, you can either just hire a local company, or read the blogs from the experts such as Googles matt cutts, although if you are a beginner, you may well find his posts a bit technical.