A close friend who has worked in several long running shows on Broadway says that whenever she's not 'feeling' it, she just thinks about all the people in the audience who have NEVER seen the show and who have trekked long distances to see it and in seconds, she's back to the very first time she performed in the show and gives her 110% to that audience --- performance-after-performance.
To spice things up for random actors, whenever I see a show anywhere (Broadway, tour, etc.), I always select a random actor and give them entrance applause. In the decades I've been doing this, I never fail to get an entire Broadway house (or theatre) to join in with me. They have no idea who they're applauding but they still join in. I love the startled look the actor gets AND it elevates that performance for everyone on stage a few more notches.
A random gesture goes a long way whenever I'm attending a performance.