Get it write.

I read a book from a mainstream publisher that had several typos in it. I found this so odd that when I came across them they distracted me from the story as I pondered the reason...staff cuts, someone rushing because of a heavy workload...I once read a self published book that told a good story in such appalling English that it spoiled the book and its chances of a good review or recommendations. The best story in the world won't get past an editor if it contains mistakes that the writer should have spotted.

Spelling and grammar are important elements of the written word. 

Your spell check won't find all the mistakes in your work and the best way to see them yourself is to print work off, rather than editing it from the screen.

Reading work aloud is another way of finding errors as is leaving work for a couple of weeks before re-checking it. Having a break from a piece of work is a good way to see it again as though for the first time. 

Create a list of the mistakes you commonly make. I always struggle to spell rhyme and manoeuvre and have to go carefully when I want to use whose or who's.

Keep the list handy for when you are writing.

Write a short story about someone who can't spell and the effect this has on their life.