Why am I so bad with Dom3

[Agema]

If you're losing, check what your opponent is doing to make you lose, and next game either repeat roughly what he did, or have a plan ready to deal with someone trying that tactic on you.

Another important point is think about what your opponent can do to you. A spell that crushed one opponent may be utterly useless against another. Perhaps the units which worked wonders on one enemy are little use against another.

One of the trickiest things to judge in a game is balancing resources. For instance mages are needed to win battles and research. You conquered a large empire with mages, but run into an opponent who can summon SCs and cast big battlefield spells like Fog Warriors, and you've no suitable answer because your mages were fighting not researching. Or maybe you used your gold to buy lots of fortifications and PD, and find your opponent has spent his gold on a huge army and you can't raise enough troops quickly enough.