I never know who starts the next trick ?
The winner of the trick leads the next card - which is fairly standard in card games.
Plus if a trick doesn't get finished and in a 2 player game lets say one player has played 2 cards and the other one who starts the next trick ?From the rules:
"If a player can no longer play a suitable potato card, he shows his hand cards and the round ends immediately."
When the round ends:
"For the next round, all 52 potato cards are shuffled and dealt out as in the beginning. All sack cards are laid
out anew. The player to the left of the previous starting player begins with the first card of the new trick.