Desicions, decisions, decisions.....
Firstly you will need to decide if you are going to paper a whole room or just one wall. If you choose a bold statement wallpaper, this should really just be used on one wall as a feature wallpaper and then paint the other walks with a matching colour.
If you are going for a striped wallpaper make sure you decide carefully which way you will have the paper hanging, vertical stripes or horizontal stripes. Stripes will be quite easy to match up as opposed to a highly patterned paper. Plain paper is even easier to hang but a feature wall really needs something special
Be sure to have a rough idea of how much paper you will need to buy. Remember, buying a fraction too much is better than not enough. Also get prepared for the hanging, make sure you have a wallpaper table, paste, scissors, a dry cloth, a brush to apply paste and a spare pair of hands to help!
Be sure to buy a paper that everyone in the house is happy with! You don't want to be changing the paper every year so make sure the final desicions is one that won't go out of fashion!