There is NO winning strategy for the kinds of situations you're placed under in HoMM 2, which is the only one I have.
On one mission, you're placed in a solitary corner of the map with one castle and literally nothing else, every single resource is blocked off with perilous amounts of random enemies, and getting to any of'em requires ingenuity and sacrifices vastly disproportional to the actual reward. Amassing any real army to combat said monsters requires LOADS of turn skipping in order to wait for your resources to accumulate. Most of said enemies are archers, meaning that it's statistically impossible to not take damage, and get nicked away. Finally, once you get past the enemies and are finally in somewhat good shape, you find that there's something like 4 other enemies on the map, with multiple castles, which are all allied, have had MUCH MORE resources and have been simply been waiting for you to bust out of your little corner, where they then all dogpile you.
It's impossible, they start with more resources, thus they'll be able to accrue the necessary unit generating buildings faster, thus will have larger armies sooner, and they don't need to worry about getting nicked to death by random archers. Plus, with the LOADS of necessary turn skipping mentioned earlier, these early advantages will snowball into unwinnable scenarios. It's like a butterfly breaking out of it's cacoon, only to see a dragon has been waiting to incinerate it before it could even see the light of the sun.
There was no forethought placed into that mission, the odds are just unfairly stacked against you, such that it's completely unbeatable.
The 'creative' maze-like levels are even worse. The game wasn't meant to be played like that.
I liked the random matches though, more fair. Well, MORE fair, as I didn't like the Ultimate Artifact system. What I mean is, since the AI doesn't need to read any of the maps, they will make a B-line straight to it's random hiding place and snatch it before you 100% of the time. The thing with Ultimates though is: while normal artifacts can change hands, Ultimates can't. Meaning if you beat an enemy that had the Ultimate, the Ultimate just vanishes and ceases to exist. It's a frustrating mechanic that seems built exclusively to deprive you of the awesomeness of the Ultimate Artifact, and I don't like that one bit.