Building a blog includes many steps.

1. Before starting blog you should finalize your niche. A low competitive niche and a niche in which you are comfortable is a good to go niche.

Find low competitive keywords for approx 20 posts in that niche.
After finding keyword write those 20 posts.
Finalize a site structure on paper including those 20 posts with categories and tags so you can implement it later.
2. Choose a good hosting not need to be expensive but should have a great response time and uptime. Don’t forget to purchase a domain which will be your website identity.
PS: Don’t include trademark words in domain unless you have license or copyright.
3. Install WordPress with light weight theme.
4. Install some good plugins for SEO, Security and other purposes.
5. Create proper site structure and save posts as draft with optimization. Don’t forget to add important pages, categories and tags.
6. Start publishing posts in a consistent manner. Be it daily, weekly or bi-weekly. But you should have a schedule.

PS : People may doubt why I said to write 20 posts first before starting a blog. This is Because I have seen many people who just start a blog but then they got lazy at writing and they close their blog.