On Page Optimisation can be called as a first step of seo campaign. Basic On Page Optimization is very important and it must be done before start of any seo campaign. Effective on page optimisation helps overall readability of website.
On Page Optimisation includes..

Title optimisation
Title is the first thing that viewer usually read and it generate small stimuli in visitor mind about what your page is all about. So, Proper keyword on title will help visitors to understand about your page and website. Similarly Search Engine also read title in a same way.
Meta Tag Optimisation
Placing Meta is very important for SEO. And it is most important factor of on page optimisation. By Meta Tag search engine robots get information about website. Proper keyword on meta tags and appropriate description is basic very important for getting your website indexed and ranked better in search engines. There are various meta tags which can be used to provide more information about website like Author, Geographical location information.
Image Optimisation
In a Simple and easy way only few things should be taken care of for Image Optimisation
Images are recognised as a external object so, it’s always better to have small size images and lesser number of images.
Image tag has ALT attribute, many search engine use this ALT attribute to recognise the image information. SO, It’s always good to us proper keyword in ALT attribute.Image Name: Relevant image name with keyword is very effective for overall seo rankings.
HTML Optimisation
Basic on page optimisation concerns are, Page should not have any unfinished HTML Tag, Proper use of h1, h2 tags (search engine treat content in h1,h2,bold tags as an important content)

Link Structure Optimisation
Navigation of website should be clean and easily accessible. There should be sitemap which can tell overall link structure of website. And No broken link should be there.

These are the basic things to do for On Page Optimisation.