There are many words that get spelt wrongly time after time. This is not an exhaustive list, but watch out for these:
afterall or after all?
after all
all and all or all in all?
all in all
alot or a lot?
a lot
alright or all right?
all right
focussed or focused?
focused
loose or lose?
Don't write loose when you mean "not win"
lunch time or lunchtime?
lunchtime
minuscule or miniscule?
minuscule
weird or wierd?
weird