Japanesse Maple

October or November, when its dormant. Keep the rootball intact if you can, break as few roots as possible, water well in its new situation, even if the weather is cold and damp. Make sure the new hole you dig is wide enough to accommodate any sticking out roots, etc., and deep enough so that the plant is buried at the same level as previously.

As bamboo says, plus partial shade out of cold breezes.
Dig planting hole square not round.
Add a mackeral into hole before planting.