The English language is filled with commonly confused words – than vs. then, break vs. brake, etc. What words do you find confusing?

The English language is filled with commonly confused words – than vs. then, break vs. brake, etc. What words do you find confusing? Why? How can you avoid making future errors with commonly confused words?

One set of common words that I mess up are their and there. I know the difference between the two, however sometimes I still misuse the word if I am typing too fast. If I slow down and think about what I am writing at that moment, I should be able to get better using the correct term. Sometimes I can get confused with than and then as well. Avoiding future errors lies in taking your time, and proof reading. If I take my time and double check my papers I will be able to catch anything I missed the first time around.