your priority should be getting power not leveling up, try to start collecting command flags to unlock assist ninjas and upgrade them, watch out everywhere it gives free myoboku packs and don't spend your moon coins on useless or farmable things, buy cave keys and wait for rebate to do either 1050 or 2100, if you are in desperate need buy the ninja assist upgrade thinggy from grocery as well, and try to farm refines as much as you can from wherever you can, grocery,space-time shop, guild shop etc

bottom line, farm power items and WAIT for their rebates

(disclaimer, this is not a tutorial, just few things to consider)