I am an adult, and am still terrible with spelling! How can I get better!?
With just a bit of effort, you can conquer this issue forever! I mean it!
First, realize that if you develop a solid memory technique, to remember a word spelling, That "trick" will stay with you forever. DO you remember all of the states or planets? If so, it is likely because a great teacher taught you a memory trick at one time!
So, take the time to gather the words that you usually misspell. And go through each one and put the time in to develop a memory trick. For example:
Do you misspell BELIEVE all fo the time? Perhaps you transpose the I and the E. Well, the trick is: there is a LIE in BELIEVE! Now you will NEVER misspell that word again.