Too often we tend to lump grammar, punctuation, and spelling into one big blob. According to Merriam Webster Online, grammar is
a. the characteristic system of inflections and syntax of a language
b : a system of rules that defines the grammatical structure of a language
There are actually several definitions listed, but I believe this one is concise and pertinent for writers.
That said, grammar isn't so important in blog writing. What I think is important is that you come across as natural-- not trying to be someone you are not.
For instance, I have a good friend who nearly always misuses the word "loose". He is a brilliant man, but someone that didn't know that might wonder how he can loose his friends. Are they in chains? Well probably not and unfortunately, a spell checker won't catch that error.
That isn't a mistake in grammar. It is a mistake in spelling caused by not knowing one word from another. My advice, as you write your blog post keep an online thesaurus handy. That will tell you if words you are unsure of are in the right ball park and can also help you find substitutes for those that don't quit hit the mark you are aiming for.
Another thing that you need to do is be consistent in your writing. If you choose to capitalize Internet, then do it every time. If you choose to put stops on your acronyms (e.g. US vs U.S.) make sure you do it always.
Develop a manual of style that contains the styles you want to use. Also include the words that give you the most trouble, such as loose and lose, its and it's, and their, they're and there.