SEO as we know stands for search engine optimisation and basically are techniques which would increase organic traffic to your website. There are so many techniques to SEO that to simplify and understand it better, it has been divided into on page SEO and off page SEO.
In straightforward terms, on page optimisation basically refers to the use of proper keywords, your use of H1 and H2 tags, page title, use of images, bolded text, italicised text, underlined text, and spaces between keywords. All these small factors optimise the search engines to search only for your website. Small factors like whether the keyword appears in the first 25 words or even the last 25 words of the page is also important. How many times is your keyword appearing in bold or in italics and what is the proximity of these keywords is also important. At a time, singular or plural keywords also hold significance as well.
The first thing is to consider that any of your website content, whether articles or blogs should not be plagiarised. If it is so then it gets penalised by the search engines and pulls down your rankings during any search. Your content needs to be absolutely fresh with well placed keywords to use them on your website. There are softwares available like copyscape premium and dupefree pro which check for plagiarism on web content. Next thing is to insert links on your web content. You can either do that yourself or take help from a SEO expert and understand how on page SEO needs to be done Many websites and blog owners allow dufollow links to be attached to your own websites. This can be easily added to your content as the search engines throws up good results if this is done.
At the same time, heavy use of flash images is definitely a no-no since search engines do not like sites with heavy videos. Always use HTML for building your website, that is a thumb rule for on page SEO. Java or load a lot of flash content on it and certainly it is a common mistake that people make. Some web content experts like to use flash content due to its presentation style. It is fine to have only a few flash content but not many since Google does not rank it high. This is because, anything like an image or other multimedia component is likely to be invisible to search engines. The search engines like Google would only recognise well-written HTML based source code and this is truly the heart of your entire web content. Hence, choose simple and effective HTML way to improve your SEO.