This is a case of “do as I say, not as I do” in that I reserved my blog’s name first, then I checked if various social media accounts had been taken as an afterthought.
If you’re smarter than me you’ll head to a website like namechk and first check to see if the domain name for your blog is taken, and secondly if the associated social media accounts (Facebook, Pinterest, Youtube, etc.) are available. It’d be a shame to pay for your domain name first, then find out someone has reserved a form of social media you plan to interact with your readers with or funnel traffic to your blog from.
You may also want to grab various usernames from certain websites you don’t plan to use so no one in the future can take them. You never know what platforms you’ll want to use.