Ok, let me explain this to you.
See, a smart clan wouldn't cast any spells before they get the message that they havent been matched. Because if you are matched, you get a message about 30 mins saying "All spells casted at this time will go towards your winnings." So if you cast the spells BEFORE you get that message, that wont go towards your winnings. So what i do is wait until i get that message and cast my spells, so i dont waste mith on a war i probably wont even go to. Then, to my advantage, i can gain more mith from TVP for Alchemist equip, future wars, ect. But thats just what i do, and i havent been in TONS of wars, so you just do what you do.