In the first place make him ordinary. This sounds like bad advice. After all, ordinary means boring, doesn't it? However, what I mean is that your hero is recognizably human. He should be credible and understandable. You need to know where he is coming from. Create a back-story for him that you find compelling and credible.
Then make him potentially extraordinary. Give him a gift. A reserve of courage and resilience that the rest of us can only wonder at, perhaps, or exceptional ingenuity, or a charismatic gift of eloquence.
At the same time make him flawed and make his flaws relevant to the goal you have set for him.
On the matter of the goal - make sure it is a good goal and that his motivation for pursuing this goal is utterly credible. Keep asking yourself: why does he have to do this thing? and make sure there is no easy get-out. Make him arc, if you can: give him an emotional journey to complete as well as a physical journey.
Make him fail. Not everything should go well for him.
If you can, build the fundamental story conflict into the character of your hero. Imagine if you will a mild-mannered librarian who has to find the strength to save the town from the alien invasion. Or the Mafia hit man who has to change his spots and become a good guy for the sake of his marriage.