Belaying a lead climber is different than belaying someone on TR.
Lead climber - Not much besides giving a good belay. Watching their movements, adjusting the rope paid out, looking for a clip => pay out rope WHEN the time is right, communicate if they look like they are getting off route, encourage them if they styled the crux. Usually nothing other than the leaders movements and actions.
Top Rope - Usually belay here is much more casual. Concentrate of keeping slack out of the rope. A gri-gri alleviates much of the required attentiveness of proper belay technique (hands free for example). Can be joking with friends, watching others climb, etc.
In general, while on belay, I know that the climbers health/life is in my hands, I never forget that.