It's tough at the beginning

It's tough because you die a lot at the start, but if you push through to around stages 3-4, it gets better. Keep watching ads whenever you can, and once you've saved up some money, focus heavily on upgrading. When you level up during combat, prioritize the 'money speed' upgrade twice first, then level up your skills. Doing the money speed upgrade first makes it easier. Ads will pop up occasionally, but you really need to watch the reward ads.... haha