Read. Books, magazines, newspapers. The more you see words in print the better you'll be at spelling them.
Write. When you read, look for words that you do not know how to spell and write them on a piece of paper or notebook.
Pratice. Practice spelling words by writing them, saying them or typing them. Use the dictionary to check your spelling. Or get someone to help you.
Spelling takes time and if you want to be a better speller, you have to practice every day. Never give up.