Not exactly stuck. More like, I have no idea what am I doing most of the time. I don't know most of the stuff in the game, or how to get better monsters, etc. No idea.
Generally speaking, almost any sort of team composition works until a little later in the game (around Castle of Satan, from what I've heard). You can poke around in the
forums to get an idea of what monsters are good or useful.
If you're against making in-app purchases, you want to aim for getting a really good dark or fire leader from your first rare egg machine roll, since most of the key members in a mono-dark or mono-red team can be farmed in later dungeons. Good REM rolls for those two teams could be Shiva, Freyr, or Ares for red; and Loki or Persephone for dark. If you get a monster that you're unsure of, feel free to ask here if it's worth levelling or not.
For most of the other mechanics, the forums I linked earlier have guides and tips regarding them. Hope this helps!