The game's difficulty really stems from two things creature and party management. Not knowing about the Late Bloomer versus Early Riser thing may make that initially frustrating. Late Bloomers have horrendously bad stats for like 99% of the game. Early Risers grow really fast and are really powerful for 99% of the game. Recognizing the Late Bloomers for what they are (bench warmers) and moving on is the essential part.
Understanding and accepting the AI is abysmal is crucial. Learning to juggle what resources they have access to as you switch characters becomes a chicken wolf grain problem. Nothing is better than switching to steal something with one character to watch Oliver cast some ridiculous spell that cost all of his remaining MP. Learning how to protect yourself from the Friendly AI, the other difficult part.
Once you master these two things the game becomes really easy.