One of the most surprising things for me is how little time you have to rehearse. In fact, TV schedules are so compressed that sometimes you meet the actors as they are walking onto the set for their first scenes.
My feelings about directing actors is pretty simple. Keep it simple. You don't want to fill the actors heads up with any confusing information. Here are some bullet points of things I find work.
Things you do before you talk to them, but you let them know:
Find the paradigm shift moment of the scene even if it isn't obvious and make sure the actors know it. Almost all scenes have a moment where either new information is introduced or created such that whatever was true for the story before this moment is no longer true now. points that out so the actors can be aware of it and change their performances accordingly.
Find as many other transition moments as possible. This could be a status shift (where one character transitions from being more powerful and in control to being subservient or it could be someone moving for gleeful to fearful. Let the actors know if you find good opportunities for this. This is the kind of stuff that makes scenes dynamic.
Things you do when talking to them.
Speak in very descrīptive terms like: "At this moment, fear to renewed determination." Sometimes you can add another short sentence why like "Becuase you realize you actually have a shot."
Speak in short sentences and then wait. Only say your thought one time, don't keep repeating it in different phrasings.
If you say something which they are misinterpreting, just say "totally disregard that note, it doesn't work" instead of trying to justify it any further.
Don't try to trick actors into doing things or performing a certain way. Just tell them what is happening.
If they are entering from or exiting to someplace - tell them where and what happened or what they expect to happen there.
If you tell them to move somewhere, help them by justifying why in a quick sentence. If you can't think of why - then that motion might not be good blocking.
Listen to actors. Sometimes they're afraid to ask about something, make sure they know you are there to aid them (be a "mirror and friend")
I could probably list many more - but these alone I find enormously helpful and... I really must sleep now. :) Waking up at 4am day after day is very difficult.