Make sure your content is ALWAYS a minimum of 1000 words. Longer content is better content in googles eyes which has been proven by many studies you can look up on your own if you don't believe me
Use keyword in H1 and H2 tags. If you are using wordpress which most people will be, this is done automatically.
Use keyword at beginning of title and modifiers or variations at end. I personally like to make my titles long, some people don't believe in it.
Example title for keyword weight loss product:
Best weight loss product review for men and women in 2018- (with "best" and "review" being your modifiers)
The reason I like to do this is because sometimes you end up ranking for all sorts of terms surrounding the title such as best weight loss product for women, best weight loss product for men, best weight loss product 2018, so on and so on.
Long titles do not mean long URLs, I keep those short and targeting the main keyword or a LSI keyword which I'll touch on in a sec.
Make sure your site loads fast. Slow loading increases bounce rate.
Add images/videos when relevant. For images make sure to use the keyword in the file name as well as the alt text. The alt text is basically what google can read from your image. Try to add at least 1 youtube video to your post if possible.
Never write your content trying to stuff your keywords. Write the content with SEO in mind but do all the real keyword adding after your content is created.
Keyword density isn't all too important as it used to be but I still use it. It only take a few seconds to calculate the keyword density of your top 10 competition to see what yours should be. Use Free Keyword Density Analyzer Tool you have to register and create an account but it only takes a minute or 2.
Use LSI keywords throughout your content. LSI keywords are words or phrases that are semantically related to each other. I'm not going to explain all about them, just make sure you use them in your content at least 3 times per 1k words, preferably once in the first paragraph and once in the last paragraph and another time somewhere else. Other good places to use LSI keywords are in your anchor text, meta tags, or page titles. Here is free tool to find lsi keywords - https://lsigraph.com/. Just type in your root keyword and it will spit them out.
Interlink content - minimum of 2 internal links and 1 outbound link per post
Some other things you want to focus on is how is your content laid out to your visitor? Is it in a good readable format? Does it keep them on the page? (along with having a lot of content)
What is the purpose of your website? Or better question, how are you monetizing it? Are you an amazon affiliate? Google AdSense? One thing that I wont go into here but that is crucial to your success is your conversion rate optimization which factors into how your site is laid out plus other factors.
If you use all of these tips, your on page SEO will be better than 99% of the websites out there.