As a writer, do you edit your own writings grammar and spelling?

Yes, I'm doing that, and sometimes also I let someone else to make a second review.

Yes, I do - at all times.  I'm very keen about grammar usage and sentence/paragraph construction. So, I see to it that I edit my work first before presenting it to the critique for evaluation.  Besides, critiques don't want to do editing; they're there to evaluate your work.  If they see that your grammar, spelling, etc... are poor, your work are likely to be rejected right away.

Yes; this would help me make my writings as clear as possible before delivering the final draft.

I at times give the draft to another person for proofreading.

I usually have the first and last corrections, but a fresh pair of eyes is always useful at picking out mistakes i may have overlooked. This  is especially true on larger projects. 

Of course I do; it makes it a better writings.

Yes, I do. I have been writing for so long, and have had so many rejections or feedback, I am pretty good at it now.

Absolutely.

Depending on the project I will also have someone look at it just to ensure I've not missed anything. 

Yes for sure. Its a must do thing.

Yes. Once the blog post is ready (content wise), the writer should do proof-reading. But before you do that, take some time away from it. Stop thinking about it. Then come back with fresh mind. It will help you proof read & edit the post.If you find it difficult to editing then you better outsource it.