Pimple for a dimple

Some mistakes are considered typical for native English speakers and at the same time are very rare when English is a second language, i.e. confusing "then" and "than", "whose" and "who's", "it's" and "its" etc.

My only idea is that native speakers first remember how word sounds and than then write it down mixing up different variants of representation, and as against to that those who acquired language knowledge from dictionary first remember its spelling.

On the other hand one of my personal very annoying problems is with prepositions and phrasal verbs. Translating literally and using Russian prepositions doesn't work, resulting in numerous silly faults. Also, there is no rule allowing to derive a right conclusion and you depend entirely on your vocabulary realizing how modest your skill is slightly more often than it is needed to keep yourself in tone.