The correct strategy for a game will depend on the game; some are deliberately designed to encourage or even force you to adopt a particular strategy. In general however, classic principles of strategy apply perfectly to Xconq. First, the words of an ancient master:
Generally in war the best policy is to take a state intact; to ruin it is inferior to this. -- SUN TZU
Attack where he is unprepared; sally out when he does not expect you. -- SUN TZU
There has never been a protracted war from which a country has benefited. -- SUN TZU
The most important consideration is to conceal your own forces and movements as much as possible. Decoys and feints are worthwhile, but only if they don't draw critical strength away from your real purpose.
Don't rush to attack with weak forces. Especially over long distances, the defender has the advantage. Wait until you have assembled enough to take and hold a piece of territory, then allow some extra, just in case.
Have a plan, and have some contingency plans ready as well.
Be ready to take advantage of opportunities.