If you are selecting pictures to hang in a group, start by using objects of similar colour and or subject matter. When grouping pictures or artwork, the selection of an odd number of objects is more interesting than the grouping of an even number. When hanging a group of pictures, place the dominant piece in the centre of the arrangement and position the remaining pieces accordingly. To achieve balance and an arrangement that you are happy with, try displaying various combinations on the floor prior to hanging.
If you are looking to create harmony in your display, use the same frame throughout. A greater impact can be created by selecting a single colour from your artwork to feature on the wall behind. Add interest by mixing the media in your display (eg. paintings, photographs, drawings) and by varying the shape and size of mounts and frames.
Art galleries suggest that the centreline for hung artwork should be 1500mm from the floor. The eye level or centreline of your artwork will vary from room to room and may be lower in rooms where you mostly sit. Your lowest piece of wall-hung artwork should be placed at least 200mm-300mm above a sofa, sideboard or table.
Heavy pictures or mirrors usually need to hang from wall studs and to ensure your pictures are hung straight always use a spirit level. Hallways are a good place to hang pictures of the same size as this creates a seamless flow in what can sometimes be a narrow thoroughfare.
You may want to consider creating an art gallery with a series of wall mounted shelves on which to place your artwork rather than hanging it. Larger pieces, particularly mirrors look great on the floor leaning against a wall.