There's a TV show recommendations topic here
I've been a little stuck with the game in the past few days because I needed new Heroes so I could train my main ones, but it was SO slow waiting for new ones to appear, and when they did the Level Up percent for my Heroes was 1-2%. I was on holiday for a few days and had more time to play and figured out the % is higher when the Hero trains against... well, themselves. 😄 And I get more of them if I go through old easy missions. I also figured out how to edit my team etc. so yeah definitely getting the hang of it now!
Also another learning is, make LOTS of health potions and just use them all the time in a difficult mission and maybe you'll get through it. 😄