Use keywords that are relevant to your content and business. Make sure they are not overused. Also, make use of them at all relevant areas like header tags, page title, alt tags, categories headings, etc.

Text content:

This is where you need to be really careful. You need to satisfy both the search engines and the human visitors. The main optimising factor here is of course the keywords. However, you are selling the product to human visitors and not to search engines. Hence, if you think a few paragraphs stuffed with your keywords is going to bring the result you want you can stop your optimisation then and there. Human visitors need good, interesting and convincing content.

Title tags:

Since the title tag is displayed on top of your web page you need to take a lot of time and care to create it. Also, instead of making it long and too descriptive, keep it short and crisp using only the most necessary words. Also, its always better to have a title for all the pages in your website.

Headings:

Another area that you can take advantage of to add keywords. Add relevant headings that can guide the users as to what the following text would talk about.

Alt attributes:

Alt attributes are those that explain an image. Since the alt attributes are loaded before the actual image itself they function as a guide to what the image will be about.

Anchor text:

Anchor texts are the clickable text links in the page. Inserting keywords as anchor text can help in optimising for users and search engines.

You can consider on page optimisation as one of the initial and crucial factors of your actual SEO process. On page optimisation more or less decides the effectiveness of the off page optimisation. Do a great job of on page optimisation and your SEO process would be much more simple and easy.