Writing SEO Friendly content is easy if your foundation is established properly. It all starts from keyword research. If your keyword research game is on point then you can write really great SEO optimized or search engine friendly content. Do good and thorough keyword research if you want to write SEO friendly content.
Your content must have 3% to 5% of keyword frequency ratio, meaning that if you wrote 100 words in your piece of content then 3 or 5 of those words must be your keywords.
Make sense to user as well as search engine. Do not write content that looks shady or spammy, instead write content that is made for the reader as well as for the search engine. This needs practice and takes some time but once you get started you can get a gist of it no time. Writing SEO Friendly content is a fun and learning experience.