If you are looking for an edge without straight up cheating I may have exactly what you are looking for. As you have probably figured out by now PokeMon do not randomly spawn. They are placed all over the map by Niantic intentionally. You may find that there are a handful of PokeMon you are having difficulty locating. If you were able to have the game open at all times you would never have to miss a PokeMon.
Now you can get notifications on your phone or smartwatch when PokeMon are near by. PokeNotify is an app that will notify you anytime a PokeMon is in your general area. What is great about this app is you can specify which PokeMon you want to be notified about this way you aren’t getting thousands of notifications for pidgeys and butterfees. Unfortunately you can’t limit the distance so you may get a notification for a PokeMon who is up to 1000ft away from you. Then again if its one you really need you may be willing to walk a fifth of a mile to get it!