Micro managing

Hi all, so I’m trying to get better at controlling my units in the heat of battle. Instead of just selecting my whole army how do i only select certain groups? lets say I have huss goons md skirms, how do i select just hassars or just goons.. Do i need to set some hot keys for this? I was watching drongo, md i seem him “cycling” through his groups of units within his army.. Also what can i do to improve my eco/raiding ? I have a problem where i get so focused on on trying to keep my cav alive/attacking that my eco starts to fall behind everyone else? im starting to think hotkeys play a roll that i seem to over look, only hotkeys i use and know are finding exploring/ idle military md tc lol