Here is a site https://domyhomework.guru/blog/homework-benefits that would help you to become a better writer. Cheers!
Best way of becoming a fitness blogger is knowledge, more you have knowledge more you will write on it. So read more and more on internet and meet experts and professionals.
The big thing is finding you target audience. Who do you want to speak to? Then how do you want to come across? Some writers scratch the surface where others get deep with their topics. All in all focus on you and what you want to write about deep down. The more you do it the easier it will become.
As Natalie mentioned, just start writing when you feel it. You can come back to anything later. Lots of stuff available out there for free to help you with platforming too. Here is a link to help guide you in this passion~Fitness!!