The on page SEO factors haven’t changed much in the last few years. The biggest change is a furhter decrease on keyword density. The article below goes over the most important on page SEO factors for 2018 and beyond.
The easy start
Best to start with having your keyword in the content. A keyword density of around 1% is considered best these days. This used to be up to 4% a few years ago so make sure you check your old content. Of course your content need to be substantial enough so 300 words as a bare minimum is advised.
Make sure you mention the keyword in the first sentence to directly start of with the right mind set. Besides the 1% keyword density use synonyms and other words related to your main keyword. The content does not have to be of the highest quality, but it is advice to have it readable and shareable for higher conversions.
Of course having the keyword in the page title is a must, preferably right at the start. It also helps with click troughs as people will quicker see that your page is what they are looking for.
Having the keyword or at least part of the keyword in the URL helps, but don’t over do it. Be especially careful when your domain name already has the keyword in it, as you might be getting close to over optimisation and become unreadable.
Having a custom meta description and having the keyword in it, plus some synonyms helps a lot. The power of a meta description is that you can write it as a nice page summary. Showing people why they would even want to click on it. If you are a business adding your USP to it will help to see people browsing the SERP why your business might be better than all the others on page one.
Making good use of h2 and h3 sub headings and adding the keyword and variations of it will make your content more readable. Use at least two h2 headings.
To keep images readable add the alt text with the keyword as a part of the alt text.
Use that keyword uniquely for one page. So not just unique content across your website but also unique keywords for all those pages. Otherwise you could simply merge the pages together.
Have inner links with the keyword as part of the anchor text like Wikipedia does.
Having relevant outbound links to sites with authority on the subject helps as well.
Roughly that is it.