Install wood paneling. A wood-paneled room often instantly "feels" like a study. Ideally, the wood should be dark in color, either a deep cherry or mahogany. If you prefer light wood, offset this by using only a half-wall of paneling and choose a dark paint color for the top of the wall in shades of hunter green, burgundy or navy blue.
Hang heavy draperies. Old-world style studies often featured heavy draperies in dark colors that were made of velvet, suede or damask. A sueded fabric in chocolate brown or tan gives a very manly feel to a room. You could also choose velvets in tones of green or blue, or a dark and complicated damask print.
Arrange a seating area. Place an ornate rug on the floor in colors that match the tone of the room. Place two leather chairs, angled to face one another, in the center of the rug. A small table for reading materials and a lamp can be placed in between the chairs. A banker's lamp with a green shade would be ideal for this seating area.
Install bookshelves. A gentleman's study should have plenty of room for books and other reading material. Choose dark woods to match your paneling for a built-in effect. For a more modern take on a gentleman's study, use black enamel and frosted glass bookshelves.
Accessorize the room. Decor items should be kept to a minimum so they do not overwhelm the room. However, small and interesting figurines can be displayed on bookcases or tables and additional lighting in the form of sconces or lamps can be placed around the room.