Once you have determined the name for your blog, buy a domain! You can purchase a domain through many places but I have purchased all of my domains through GoDaddy. I know many people who use BlueHost for hosting their blog so they also get a domain FREE. Either option is a good one!
I would also encourage purchasing the .com, .net, and whatever other dots you think are applicable. Do a search and see if any come up. Search in google – never search on one of the domain sites because chances are if you do that domain will be GONE soon after! I think they have robots buying up searched domains or something (not sure if that's true but did you notice I'm not a .com? I have since acquired the .com but just grab it in the beginning to avoid what I went through :)
Also, purchase any other name spelling variations. A blogger I know has an “S” on the end of her domain. Another person purchased the domain without the “S.” Whatever reason this happened is irrelevant. The other person surely received hits from people inadvertently leaving off the “S” in direct traffic or google searches for that domain name.
When you buy the domain, it's easy to get it set up with transferring to your blogging platform. Your domain service will be able to walk you through the steps.
Action Plan: To echo yesterday's tip on naming your blog, now you just need to buy the domain for your blog name. Buy any variations that are relevant too. Think in the future and buy up other sites that could be spin-off sites for your blog.
Now your'e ready to Create Your Blog and Blog Design!