What are some troublesome verbs?
I suppose by this you mean verbs often confused. Three pairs come to mind right away:
lie, lay, lain & lay, laid, laid: The first refers to someone putting himself in a reclining position; the second means placing an object (putting it down). Note that the simple past form of the first group is the same form as the simple present form of the second.
find, found, found & found, founded, founded: The first means to locate something which was lost or misplaced or to come up with a new idea (Eureka!): the second means to create an institution. Here the simple present of the second is the same form of the second and third of the first group.
hang, hung, hung & hang, hanged, hanged: The first means to suspend something in the air or from a vertical support; the second group refers to lynching someone.
Other verbs often misused are those in the subjunctive mood. They express hypothesis or theoretical situations rather than facts. These are most often used in the context of conditional sentences.
It's high time we had an inventory of all the stock.
If I were you, I wouldn't notify the police yet.
In these particular examples the second verb form is "borrowed" to express something other than the simple past tense.