"As soon as it is available, build the structure that will allow your race to improve resource production (market, trading post, mill,...).  Pay for the upgrades as soon as you can - it will pay huge dividends as the game progresses." - TEM

"When playing as the Fey, build multiple keeps.  Since a good portion of your units are produced by the keep, you'll need more than one to quickly build a large force." - TEM

"It is a good idea to select one of your race's builder units as one of your starting units.  When the scenario opens, have the builder begin on your keep and have your hero immediately convert nearby resources.  If you are starting with just a hero, build the keep first, and then have it create a builder unit while you move your hero to convert resources. " - TEM

"You don't need to convert enemy resource sites to deny the enemy the resources there.  Send some regular troops to attack lightly guarded sites and make the sites neutral.  You won't benefit from the site, but if your hero and generals are busy, then at least you can hurt the enemy's production. " - TEM

"In Campaign play against multiple opponents, it is often possible to completely eliminate one enemy right away just using your hero. This will allow you to then easily defend your encampment against the other(s) while you build your forces." - Wild Willie