Assume your three most common errors are these: “teh” instead of “the”, “yors” instead of “yours” and “cputer” instead of “computer”. You can define abbreviations for these. An abbreviation is a word which Emacs will translate into another word, as soons as you type a non-word character. If you type t e h SPC, for example, Emacs will translate this into “the “ – which is exactly what you want.
See this Lisp:autocorrection_abbrev_defs for some more common auto correction abbrevs.