Every action has an equal and opposite reaction. When your characters start using magic, they must be made to pay for it in some way. If it is effortless, it isn't real, and no one will believe your story. If your hero does good magic, the use of this magic will have a detrimental effect somewhere. Conversely, your villain's magic will have good fallout somewhere.
Actions have consequences.
When you make your characters pay the price for their actions, when you make them both culpable and responsible, you have made them real. Give much thought to how the good and the bad of what they do affect them, and write this. The most obdurate magical stone wall created by the mightiest evil wizard had better have a crack in it that a determined, intelligent hero can find with effort. 4.It ain't that easy. The glorious hero had better not be able to find it by picking up a convenient book and, without having any prior magical training, reading the spell that will bring the wall tumbling down.