Macro = manage the game as a whole: controlling resources and long term objectives like your economy and your global strategies and options throughout the game (build orders, timings, knowing when to attack and when to play defensively or what area of the map to prioritize at any given time in the game etc).
Micro = managing your units at a more individual level, constructing your base managing the space that is right in front of you tile by tile, and controlling them units. Basically having good reflexes and knowledge of what units can do.
Warcraft 2 really is quite balanced of both side of the spectrum if you have good reflexes chances are you are already be good at the micro part of the game and be pretty fast I would recommend spending more time on the macro, planning and adapting your strategies controlling the directions the game can take.
If however you are a pretty slow player chances are you are focusing on the macro part of the game a little bit too much (build orders etc) and can improve trying to spend a bit more time controlling the units you have.
Unlike many modern real time games having good reflexes and being fast in warcraft 2 will not be enough to make you a strong player, war2 is much more balanced in that regard you need both skills it will reward a smart player for making the good decisions too.
The strongest players in war2 are not the fastest ones
The best way to improve still is to maximize the fun you get out of every game win or loose though