One of my favorite mobile games.
Tips:
Early on money matters less, and using troop efficiency matters more (anti light against light armored enemies, etcetera). At higher arenas, each wave has a higher max unit send limit, so money matters more. At higher arenas, start sending newbies, the cheapest troop, so that you have more money in future waves.
Also, when you have 1400 gold, select the 1500 unit to hold money to send later. you can do this to retreat, or send zombies so your hero is defended while it attacks nearby enemies. Spectate 900-trophy players to see how they do this, in “Watch Battles”.
There is a lot of strategy involved, game is deceptively simple. Pick the hero you want, unless you want lvl 30 crystal. Focus on leveling up hero to get more HP and troop bonuses, glyphs are next important, followed by hero equipment. Boarfighter and Battlecat are best soldiers and try to get them with lvl30 glyphs (5 tier 6 glyphs) as soon as possible.