As a technical director, myself, speaking from the other side of the fence.  I would be sure you know what the set will look like  as well. (given that there is one)

I recently worked with a director who ignored everything I told her.(some changes just had to be made due to space and what not) The actors ended up changing blocking a week before the show! It was extremely hard on all of us, especially the actors! 

Being in contact with your set designer/builder I think is very important.

May not be the advice you were looking for, but something to keep in mind non the less.

Good Luck!

Although I know a few things ahead of time I ussually don't have it pre-blocked.  The reason being that I want the actors to be part of it aswell.  I want to see what they naturally do on stage.  And then I will change it and fix things after the first few rehearsals.

I like to give the actors the chance to find things themselves and also - for me - it's a lot easier to work with real people than to try and envision it all beforehand.

So for a newbie I would say - try to block it ahead of time to see if that works for you but be flexible and trust your actor's instincts as well.

Know what the set will be like first to stage.

You can work in advance on character development and know what you really want. 

Outside of that give the actors some freedom/within limits (I agree ChuckK6)

Trust your instincts.

Blocking is an extension of the play.  Where do the actors move about the stage as they say their lines.  When I direct, I usually read the script about a zillion times, hearing the voices of the charactors, and the look for the feelings of the words being said... And once I know what the stage is going to look like in my head, I block.  I take a pencil and go through the script again.... Character A... Moves down right to table.... Character B.... folds his hands and stands on his head as they say...   But most is just general blocking, and I always look for a reason why the Character is moving from point A to Point B.   Perhaps the Characer forgot to pick up something from the table and needs to get it now... or Characer A, just said something to Character B, that forces Characer B to make a move either towards or away from Character A...

When and if you know what the scene is about, the Blocking generally flows from the mind to the written page and to the stage...

I do try to give the actors as much leeway as possible, but sometimes, as we go through rehearsal, I'll see something that if they moved a certain way, or went for the chair or sat a certain point, would help in the drama of the scene.   And sometimes I just sit and watch my actors, as they are already doing exactly what I want the scene to do, and they are moving instinctively and in tune with the scene presented...

The other thing you have to remember is you as the director are not only setting the scene, its tone, but also the stage pictures, what do you want the scene to look like visually?    At the height of the scene, where do you want everybody to be:?  How much weight on one side of the stage do you want?  Where do you want your actors to be on stage when the climax comes? 

I hope this helps in the disscussion.

Steve C