Mother-tongue English speakers, particularily North Americans, are infamous for their bad spelling (present company included). This is why the Webster American Spelling book is the #3 most sold book of all time. 

Only Mao Tsi-Tung's Red Book and the Bible have sold more.

It's also why Spelling B's http://en.wikipedia.org/wiki/Spelling_bee are so popular in North American schools.

Here are three simple tips to help everyone improve their spelling in English:

1. Read anything you can find in English...A LOT!

2. Make a list of your commonly mispelled words

3.Use Mnemonics. Mnemonics are memory tricks or devices, like “i before e except after c”.

For more detailed info, have a look at this website

http://www.lifehack.org/articles/communication/how-to-improve-your-spelling-skills.html

CHEERS!