The microphone moves to within 2-3 feet of the actor and stays there. Each take focusses on the actor you're currently focussing on, not moving the microphone at all... if your shot is a two shot - obviously, the microphone won't be able to be that close to your actors or it'll get in frame... I like to boom down between them then and turn the boom from one actor to the next BETWEEN their lines of dialog. the actors should be putting gaps between lines for the editor to cut (film is not stage). If their ego says, but we're in the moment -- that moment doesn't exist on the screen, leaving gaps will allow the editor to make them look as good as possible (generally the editor decides when an actor will cut the other off by overlapping their dialog).
At the end of each scene you're shooting, get a solid minute of silence recorded... everyone on set is SILENT and the microphone records the ambient noise of the place.
When cutting your dialog, remove everything but the dialog from the tracks. Then place the "room tone" (silence track) under the dialog between the pieces of dialog. You can fade into and out of the roomtone to make it less noticeable where those start and stop... just make sure that the fades start and end before the edge of the clip.
boom, decent dialog tracks without hard cuts... just putting in the room tone will do an amzing thing to your audio if you do nothing else between the cuts.
Perception counts too, J & L cuts (starting audio before or after the picture cuts) will motivate the cut and the audience will notice the cut even less... when they both change at the same time, it can be jarring... making the audience WANT the cut helps them accept the change more easily.
Psychologically, if we hear something, we want to see the source of the sound -- hardwired to do so, survival and all that. start the dialog, then cut to the actor after the first word or two. You'd be shocked at what you can get away with just using the J cut. With the L cut, the picture cuts first, then the audio.. generally used to show a reaction to what's being said by the other actor... again, the audience has identified the source of the sound and now WANTS to see the effect the words are having emotionally on the other person/people involved... if you can cut where the audience WANTS you to cut, you'll be able to get away with alot more in the edit.