Units of level 1, as mentioned here, are very helpful. And it is also desirable that these level 1 units are not from Sylvan's castle, in order to minimize losses. I usually buy another hero from a different castle in the tavern, along with his troops, and they become such level 1 units during the initial exploration. It is better, of course, to take good heroes as well. If a necropolis or demon appears as the second hero in the tavern, I don't buy such a hero so that morale doesn't drop. About splitting the archers, this has already been said, and it is correct in almost all cases, except when the opponent is not a very strong melee fighter of level 6-7. In this case, it is better not to spread out your forces and surround the main attacking stack with supporting units.
I also noticed that the development in the first week and the types of neutral creatures in the mines are decisive. If these are melee fighters, even strong ones, then there are fewer problems, but if, for example, they are druids, succubi, or mages, then if you are a little unlucky, the losses can be very serious. Logistics also helps a lot on medium and large maps; you can get to the opponent and resources earlier, and if you are slow and develop slowly, then well-developed logistics helps you quickly catch up. I take it right away, and recently I have started taking scouting with Order and Upkeep. Of course, this is not for maps like "Former Friends"; it is not needed there at all.
With archers, level 1 units, especially fairies, help not in defense, but in attack, to cover the archers. If morale works, then it is possible to cover some stacks of archers with these level 1 units, and the other stacks will defeat our archers. As a result, only the level 1 unit is lost, but it is still a pity, since every warrior counts for the elves.
For example, on "Disputed Island," it is better to defeat phoenixes with archers, ents, and nymphs. Phoenixes are fast, they regenerate, and they have a fire shield. And ents are tough, and it's not a pity to lose them. My opponent, playing as humans on "Disputed Island," suffered serious losses when defeating them. And I took only forest archers, 2 stacks of ents to cover them all (I had Wing with the tactics skill), and nymphs to regenerate the ents. The losses were minimal.
I'll write more if I remember anything. Recently, I have become good at playing as the Elves on the "Yubileynaya" map.