People seldom mix “two” up with the other two; it obviously belongs with words that also begin with TW, like “twice” and “twenty” that involve the number 2. But the other two are confused all the time. Just remember that the only meanings of “too” are “also” (“I want some ice cream too.”) and “in excess” (“Your iPod is playing too loudly.”). Note that extra O. It should remind you that this word has to do with adding more on to something. “To” is the proper spelling for all the other uses.