Read this in the early to mid 90's. This was almost certainly the first installment in a series, as it ended in something of a cliff-hanger.
Our hero wishes to live the easy life in an unassailable castle or some such. To bring this about, the hero goes on a series of quests.
First quest is about defeating some faerie based witch/medusa. It resides in a castle filled with the remains of its victims. The hero goes in, grabs a metal object from a dead victim and because he guessed right that the monster is a faerie uses it to defeat the monster. He then becomes the owner of the castle.
For some reason I did not understand, this did not make him satisfied. Instead he took some object from there (I'm assuming) and went off to defeat the four elements?
The book ends with him defeating either fire or water and going off to fight the other. Again, by using his brain and trickery against impossible odds.
I don't doubt most of the details are wrong. Googling it is a pain. However, I suspect this is pretty easy for someone who read it to identify, as the plot is pretty distinct.