get a notebook. write down 5 things that interest you. now choose one thing among those 5 which makes you happy. write a blog on that topic.
You should get a decent domain, hosting, install wordpress and configure the plugins. There are plenty of good tutorials on web about that. Next is content writing and link building, based on your budget, experience and expertise, you can do them yourself or outsource them.
Decide on which category you would like to create a blog., try to find relevant posts, you should need lot of contents, be specific @ your ideas and plan according to it
I would suggest getting a free wordpress or blogger account first before you spend money and time on a paid domain, hosting, etc. You can always move it over in a month or two, assuming you are still interested.
- get a domain name - get a hosting service - install wordpress - write - promote - intract with your competitiors - build a name
Choose the topic you will be writing about. Prepare some posts on that topic. Get a domain and hosting. Advertise for better results.