Spelling was mostly a matter of personal taste before the nineteenth century, and some of us are still rather loose in our spelling habits. However, standard spelling conventions were introduced to provide greater clarity in the language. The principal goal of writing is to communicate ideas to the reader, and communication is best accomplished without the distraction of unusual or incorrect renditions of words.
The first step in learning how to spell more accurately is to want to improve your spelling. Consult a dictionary for the spelling of any word you are even slightly doubtful of. This may seem like a lot of trouble now, but it will save you much grief in the future. And while you are checking the spelling, check the meaning of the word too. You may be surprised!