The English spelling system is a real mess, so it is hard to give clear advice on this. However, you are on the computer all day- what sort of work are you doing?
Try to keep track of your repeated mistakes.
Which of these would you use:
definately/definitely
separate/seperate
accomodation/acommodation/acomodation/accommodation
These are fairly common ones that people have trouble with. If you could give us a few concret examples of words you repeatedly have trouble with, we could make some more specific suggestions.
Also, as a cheat, always refer to your spelling mistakes as typos.
