Tips on tactics and development in Heroes.

I've been playing Heroes extensively since the 5th installment. I played the 3rd game a bit back then, but I spent most of my time on Disciples 2, which had its own unique features, like not being able to capture cities. So, my skills in Heroes weren't very developed. I play decently, but I'd like to improve. Could you please give some advice to beginners or those who play well but want to enhance their skills in this fantastic game? Specifically, regarding the optimal city development in the early game – what should be built immediately, and what can be postponed? What are the advantages of hiring 4 heroes? Which units should be used for defense, and so on – even just a few general tips would be helpful. I'm interested in advice for the Academy and the Dungeon.