How could nostrils be made less noticeable? I dislike my nose from the front because I feel my nostrils are too visible (photo)

From the photograph you have provided you have good nostril symmetry and normal visibility - the nostril rims and the skin between the nostrils should look like a "gull in flight".  Lowering you nostrils would be difficult so on the basis of this one photograph I would advise leaving them alone. I am sorry if this is disappointing.

Hello and Thank you for the question, 
It is difficulty to give an assessment with a single view. A profile view would be helpful to determine if you have a prominent columella. If this is the case a rhinoplasty may be helpful. 
Hope this helps and good luck!
Dr. David