Do On-page and OFF page optimization with Seo Rules and Guideness,
Create Backlinks to your website
Try to get more Traffic through SMO

You should write at least 500 and above. I would recommend 1500 tho. I wrote a post on how to improve a page rank by using keywords effectively so you might want to take a look: bit.ly/2dyHE8v
To cut it short, make sure that you tag your posts, use keywords in picture and video. And Dont' over use keywords.

There are 200 factors involves in google search engine ranking. Try to make your website as friendly as as possible for users. Provide better user experience & relevent content to the user as well search engines. Your website will be pushed to first page by search algorithm.

Target relevant keywords.
Give the page a name with a title tag.
Entice visitors with a meta description tag.
Add in a header (H1) tag with the target keyword.
Include keywords in relevant, comprehensive page content.
Make sure website navigation is clean, reliable and intuitive.

When you go to optimize any keywords in Google, you should do research on proper keyword research. After that, you need to do on-page optimization for the website. When it's completed, you should go to make quality backlinks. Through this process, you will be able to promote your keywords on the search engine.