Tips:
-Master the art of finding and defending optimal gyms.
-Pace yourself to avoid wearing down all of your Pokemon. Sometimes it's best to pass up an enemy gym or a raid.
-Spend gold on clothes, space, and passes instead of items that can be found at a Pokestop or gym.
-Work toward a gold badge in at least one gym with a reasonable level of competition in order to gain better items from it.
-Manage the space in your bag to avoid needing to expand it.
-Use wild caught Pokemon with a decent cp level as pawns before tossing them out. This will give your main Pokemon a break and help save valuable healing items.
-Consider clearing level 1 or 2 raids if you have free passes to spare.
-Don't forget you can earn one free pass a day and hold one pass which means it is possible to use two free passes in a single day.