David Ogilvy, the businessman considered to be the Father of Advertising said:
“Do not address your readers as though they were gathered together in a stadium. When people read your copy, they are alone. Pretend you are writing to each of them a letter on behalf of your client.”
Of course advertising and letter writing has changed quite a bit since then, but the basic sentiment is still valid. When writing copy for your website imagine you are writing to one person who is genuinely interested in your service. Don't get too casual - I don't recommend writing website copy like a text message. Keep it simple and easy to read, but don't mistake formal as the only proper tone. Don't be afraid to rewrite and try it a few ways. Get some feedback from your friends. They all visit new websites everyday. They can probably give a objective opinion.
For example: Sometimes it might be more friendly for you to write the "About" copy on your website in the first person instead of in the third person. This might be more suited to your particular business or blog.
It's always good to put a little personality into the copy on your website and especially in your social media posts.
Also, one last tip: Read your website copy outloud. When you do that you'll be more likely to find any flow issues and typos you might have missed.