Sometimes you just have to learn to spell words. But how? One of the most tried and tested methods for English-speaking children is look, say, cover, write and check ... and it works just as well for adults.
LOOK at the word you want to learn, and I mean really look. Which bits of the spelling are easy and which are not so obvious? Mark the 'hard spots', that is the difficult part of the word, using a different colour pen. Is the word similar in spelling to another word that has a related meaning? Can you break it into parts?
Have a really good look and think about the spelling until you feel you can spell it.
SAY the word, while looking at it. Is the spelling a reflection of the sound? If not what is different?
COVER the word with your hand, a piece of paper, your coffee cup, the cat or whatever. Close your eyes and try to 'see' the word in your head.
CHECK your spelling by uncovering the word and comparing it with your spelling. Check it letter by letter. If it's wrong, start again; if it's right, have a sip of coffee and tell the cat how clever you are.
Even better, do it online - then you can't cheat! Here are some great websites to help you.
My favourite is Ambleside: http://www.amblesideprimary.com/ambleweb/lookcover/lookcover.html . It's so simple and you can put in your own words. For adults as well as children.
This one from the BBC is fun and full of surprises but you can't put in your own words unfortunately. http://www.bbc.co.uk/skillswise/words/spelling/waystolearn/lookcover/game.shtml
There are more sites like this. Let me know if you want more or know of more yourself.