Step 1) break the portals so that players no longer feel that every purchase is worthwhile and improves their team.
Step 2) introduce Aether as a compensation for step one with the promise that aether will always be great. Then just ignore updates to the Aether shop making Aether almost worthless to your top supporters.
Step 3) introduce runes (actually not a bad idea) but make rune crafting expensive and based on gambling with limited success for non cheaters.
Step 4) try to eliminate F2P players by discouraging slow leveling even though they are an important component of the game for those that pay.
Step 5) change PvP based on complaints about bait teams so that only the top couple hundred players feel they have a chance to compete. Make sure the rich get richer and the poor get poorer.
Step 6) Nerf the heroes that the best supporters of the game have spent money on and have maxed. After all, they should have known better than to waste money on a mobile game and the heroes should never been designed that way to begin with. Laugh at the players that wasted money on them. They have more money to spend.
Slept 7) make PvP streaks to encourage cheating and make PvP a grind. Limit the cheating to Android users. After all, everyone hates Apple corporation for and players found PvP the most attractive part of the game. Players shouldn't attack teams that they find challenging and fun. They should only attack teams that they think they can beat to continue their streak.
Step 8) antagonize players by ignoring bugs which end streaks including crashes and the OP heroes like MK having critical hits while diseased. Just tell players their complaints have been passed along. If they complain to customer support, just tell them it is probably their fault. They should probably just buy a new device.
A game with 100 players spending $100 a month is not near as good as a game with 10,000 players spending $10 a month.