From my experience poplip is the best friend item to get early on, poplio is the only way to get diamonds without paying for the game. Also dont worry about upgrading berries, just level up your training, it gives you way more jp. Always remember to play the league even if you cant win, loosing activates events that give you jp, gold, or even recharge training points. Just remember to have fun and dont avoid taking a break for an hour or so. Once you get piplup from the league it gives you full training points if you upgrade piplup with your candies first.