My driving instructor told me that as a general rule of thumb, if it is after 12 o clock then use the right hand lane, before 12 o clock use the left hand lane, unless the road markings say otherwise, no matter how many exits.
Although my Nana's method was much better, just use the left hand lane for everything
That's only a minor part of it though, so if that is were you failed, then you're dead set for next time