thank you for the warm welcome chubb and shing!!
try using the bulbapedia guide or the voltorb flip calculator to increase your chance of getting more coins!
if you mean tips for the game in general though, i'd say if you're keeping to the level cap, try leveling up your pokemon to around 1 or 2 levels below the cap before a gym battle (so for example, if you're going to battle venam, try getting your pokemon to level 19 or so), and keep around 5 reverse candies on you at any time-- you don't know when you might need them. Oh, and keep your team balanced in levels because if one of your pokemon starts hanging behind, even if it's just 2 or 3 levels, it'll be a lot less useful in later battles.