How many times have you interchanged your i's and e's after the l's and the c's? Just remember LICE ... as in believe, relieve, conceive, deceive ...EXCEPT for the words ancient and science.
I used to have this problem when I was at school, but I guess the old saying, i beofore the e except after c works most times and I think being on sites like this really does help one with their spelling.