Be Perfect at English Grammar and Spelling

It doesn't take a rocket scientist to know that English grammar and spelling will have a lot to do with keeping the interest of your readers. If your readers have difficulty understanding your content because you are not proficient in the English language it can hurt you in the long run. People won't come back and re-visit a blog that they can't understand. If you are not a native English speaker you have a couple of options.
1. Pay someone to proofread your posts before you publish them.
2 Take ESL language courses (many times they are free).
3. Study on your own with self-help English grammar books.
4. Invest in Rosetta Stone for English

The benefit of having perfect grammar and spelling will be that your readers will come back if you are writing content that gives them value for the time they spend reading.  If you chose the option to invest in Rosetta Stone, keep in mind that there is American English and British English.  If you are going to write content for an American audience, then get the American English version.  If you're writing for a British audience, the get the British English version.  I can attest to the quality of Rosetta Stone, as I have used it to study Russian and my Russian wife has used that in conjunction with ESL to study English.  We have managed pretty well in being able to communicate with each other by using these two language aids.