On location what you’re mostly going for is clean, consistent dialogue. Ideally every actor is recorded at the same level, with the same tonal quality and presence, and with no unwanted background noise. First step is to listen to the location. There are two kinds of noise you have to be constantly on the alert for:
1. Constant low-level background noise like air conditioners, fridges or other machinery. Turn these off if you can, though often in a commercial location that’s not possible. If you have to live with it, then try to ensure it always sounds the same no matter which direction the mic is pointed. And be sure to get a ‘wild’ recording of the background noise on its own, which the sound designer can then use to smooth things out in post.
2. The other type of noise is the intermittent, irregular kind. Background music, busy roads, flight paths, noisy dogs or birds, and so on. Most of which you can’t control. Murphy’s Law ensures these noises will happen right when you least want them to. During a take and right on an actor’s most crucial lines of dialogue. Ensure the mic is aimed to get the best dialogue while rejecting any possible unwanted sounds (ie: at the beach face away from the crashing waves). Also during each take listen carefully for when a noise occurs. If it isn’t right on a line of dialogue it can be replaced with atmos in the sound design later.