1. There is no best mix or perfect combination of cards to create the ideal deck.
2. But by following points of Clash Royale cheat sheet a player can create an efficient deck:
a. Include few of every type, troops, hero cards, spell and building.
b. Also consider elixir requirements of every card before selecting.
c. Have minimum two-point damaging inflicting cards such as Musketeer, baby dragon etc.
d. Mix of ranged and melee troops.
e. Include not more than two air targeting cards such as Witch, X-bow.
f. Have one defence structure card such as Mortar. You can try hacks from Metodologic.com.
g. Calculate average elixir cost and make according adjustments.