Magic use to be prevalent only in fantasy novels but more and more, magic shows up in other genres, including romance and suspense. Magic can certainly enhance a story, but you need to make sure it is believable. You need to clearly define what can and cannot be done with magic. There must be limits on magic otherwise the person using magic would always win and there would be no conflict in your story. Magic cannot be the answer to everything. Or as Rumpelstiltskin in ABC’s Once Upon a Time said, “All magic comes with a price.”
You as the writer get to decide what that price is. If the magic is an innate talent, the amount of magic one can perform can be based on the physical or mental strength of the user. It could be restricted by the person’s knowledge or imagination. Or perhaps energy is taken from the spell-caster to power the spell itself so performing magic drains the user. Or maybe the person draws on magical fields, and once those fields are depleted no more magic can be performed in that area. Along the same lines, maybe there are magical lines running through the ground and magic is strongest when you are standing on or near one of the magical focal points.
If the magic is acquired through studying incantations and spells, then the magic might be limited to what spells that person has learned or the wizard’s access to those rare and exotic books. Perhaps each magic user has a certain allotment of spells that they are allowed to use and when they have used them up, no more magic.
Another way to restrain how often your characters use their magic might be to have the act of performing magic create a “sound” that other sorcerers can hear. As Dumbledore notes in J.K. Rowlings’s The Half-Blood Prince, “Magic always leaves traces.” In that case, your character now has to be selective of when and where they perform their magic and it becomes part of the conflict.
The possibilities of how you limit the magic in your novel are endless. But you do need to establish your rules of magic BEFORE you begin writing so that your story builds off of the character interaction and not the easy use of magic to solve the problems. Be as detailed as you want and work with the idea that your reader may never know all these “rules” but know that by establishing your magical system you are creating a more believable magic and a more believable plot.