The maps I make are all standard, that is, no changing of status of any unit or structure. However, there are actually ways to make balance changes in standard maps. For example:
Nerfing Orc Blade Master: Put an neutral Owl Scout on the Goblin Merchant.
Buffing Undead Crypt Lord and necromancer: Put more critters to provide corpses.
Making Undead expansion easier: With certain arrangements of doodads, the expansion gold mine can be sealed with only two Ziggurats. In this way there are more possibilities for undeads to expand especially with the presence of Blademasters or Paladins.
Nerfing Human fast expansion: Simply put stronger creeps on expansions.
These balance changes are based on the performances of currrent top players. Still, the importance for maps to be standard is that they can be accepted by pro players. Some of my maps are actually used in some small leagues in China, to be played by pro War3 players.
There are also new elements that can make maps more interesting, like Goblin Shipyards and Way Gates. The dragons in Dragon Roosts are found to be too imbalanced so we don't put Dragon Roosts anymore. Different tilesets from WCG maps can also be interesting.
I am still looking for ideas for balance changes and ideas to make maps more intersting. Please share if you have any. Other ideas regarding melee map making are also welcomed.