I tend to declare what they appear to be doing, while only I know what they are doing. . . .overly tactical games where you get "And the invisible assassin you can't see intends to come around the pillar behind Joe, and make a full OB attack to his back." can be a bit of a buzzkill.
I tend to write down stuff if it's a big combat, like when I say "The two orcs advance with swords in attack position." I might jot down "Orc 1 40/20 OB/DB on joe, Orc 2 40/20 on Billy". . .and I tend to decide and write down splits before the PCs declare them, but don't tell them, because I tend to find that to be too much info sharing with the PCs.