I tend to use the following:
Space, 3, 5 - tell everyone to fire at will
Space, 7, 3 - tell everyone to be aware
When I hit combat: "Space, 7, 2" - tell everyone there's danger and they go into combat mode, using cover and providing cover for movement. After the engagement is over I then use "Space, 7, 3" again to tell everyone to be "aware"
Something also useful is to use the F1-12 keys to select an individual unit, then "Space, 2" and a number to give them a target. I allocate targets to my units and they'll usually do a good job of dealing with them. When the engagement starts sprawling a bit I use Space, Regroup to get everyone back in formation.
For AT, select the unit using the corresponding F key, and then tell them to engage the target "space, 2, [target number]"