Where do you hire contractors/freelancers from?

I wanna hire someone to perform certain tasks for my business, but I don’t know where I will find the right people.

I am concerned about their skill level as I need someone who can actually do the stuff they say they can do and get me results.

Take SEO for example.

I want someone who can get my website to the first page and even to one of the first few search results on Google.