So, after talking to some of my fabulous clients, there are a few things that are reoccurring, besides the obvious - good audio and video. I guess I'd classify them as general service items.
1) Timely responses. I often get a "Wow, that was fast." Fast response to emails, fast return calls, fast quotes. I don't like to wait for someone to get back to me. Why would anyone else want to wait? A cell phone does it all.
2) Troubleshooting. There are problems, all the time. Your fault or not, it's still a problem, and it needs to be solved. The blame game is meaningless to the client. Fix the problem and move on. Your client will appreciate your quick problem solving skills.
3) Arrive before call time. Being ready to roll 15 minutes early puts a smile on everyone.
4) Not "nickel & dimeing." What does it cost you, if you have a slider in the truck, and you can add a little movement to your interview? Nothing. A client sees that as a bonus. They appreciate your efforts to add production value, and they'll remember that next time they need a production.
5) Preparedness. "I'm so glad you brought a fan!" Well, we are shooting outside, and it's hot. Let's keep the talent as cool as we can. Think about whatever you might possibly need for your shoot, and bring it.