If you're bad at spelling it may be due to storing words as audio rather than a visual picture.
Phonetically words can be spelt lots of ways (fone, foan, phone, phoan ect.) but only one is correct, and that can only be known by storing it as a correct visual in your head.
I always thought as long as it's readable it shouldn't matter, but if it does that might be a good place to start. Learn to visualise the words instead of relying on the sounds that make up the word.