Spelling improves slowly. There's no quick hack — but there are habits that genuinely move the needle.
The classic four-step
Look at the word, cover it, write it from memory, check against the original. Repeat for incorrect ones. It's worked for sixty years because it teaches the brain to encode, not just recognise.
Target the patterns, not the words
Children who learn that "-tion" makes a 'shun' sound, or that double letters often follow short vowels ("dinner", "summer"), make faster progress than those grinding through random lists. Practice now with spotting-style spelling questions.
Read aloud
Children who read aloud regularly hear themselves stumble on unfamiliar words and naturally pay more attention to how they're spelled. Five minutes a day is enough.