For dominions generally:
Have a strategy of sorts for the long-term. Make sure you can expand to at least 10 provinces within the first year or so- figure out how your nation can effectively expand, and ensure one of those strategies is enabled. (ie, for Yomi, I dislike their gold-expensive troops for early expansion, so I started with a SC pretender) and have at least one midgame strategy and lategame strategy in mind. Have an idea of how you might counter the most common early strats, or at least blunt them. (astral nation with no significant SC counters? Research horror mark. Now you've got a deterrent, if not an effective weapon.) Research and gems are somewhat more important than gold later on, but gold has its uses. After that, play dynamically, not too conservatively, or you will fall further behind. Don't give up from setbacks, and shift your guns. For fighting any player that you can't take out in one go (and you usually won't be able to do so) have more than one strategy planned, as a player can make hanging on to the same one very expensive. Surprising your opponent with an innovative strategy can be helpful, and at a certain point, you might even start researching specific spells specifically to deal with certain threats - like MindHunt to deal with a non-astral invader, or witherbones v. Ermor or c'tis.