So here's my lil strategy for beating normal, first time playing:
Spells are most important, I repeat! SPELLS ARE MOST IMPORTANT.
That being said..
1. Upgrade your manna as early as possible.
2. Troops will be won from battles so don't worry about buying them. Keep a nice mix of range and melee, in the end my army consisted of demon warrior, mike t thrower, superman fighter, and pbot tanker.
3. Upgrade weapons as you please and pay attention to any troops that will increase your stats.
4. Next most important spells are regenerate and defense. Cast these two together and your army will be virtually unstoppable if you keep them refreshed.
5. Later, a crucial spell is resurrect, where casting on a grave will bring the soldier back to life. **This can be used on enemy soldiers to add them to your own army, giving you a massive army over the 8-army cap**
6. Make your 8, defend and regenerate, resurrect, repeat!
7. On hard bosses, use your freeze spell.
Enjoy and keep this post alive!