Always view the wallpaper in the room it is to be hung in. Hang as large a sample as you can and then take your time. Sit back and take it in. Come back in a few times during the day to witness the different lighting and see if it has the same impact on you.
Perhaps your room is lacking a certain punch? Why not take a chance and let your wallpaper be your statement piece. If you're opting for a particularly bold print then just highlighting a section of the wall can be a good starting point.
You might have some key pieces of furniture in the room and simply want your wallpaper to compliment them. In that case, a simple elegant colour or print is your best option.
For small spaces choose something with a lot of intricate detail. For larger spaces, it's okay to go all out with bolder patterns.
The first strip sets the path for all the rest so that's the one you need to get straight. The heavier the wallpaper, the easier it is to hang. Paper and vinyl wallpaper require different adhesives so make sure you know what you're dealing with. Order more paper than you'll need to allow for mistakes and to keep some stored away incase it goes out of stock.
Remember to mark out wall outlets and attachment holes you need with wooden toothpicks so you can find them again. If it's your first time hanging wallpaper, than a pattern that needs to be matched up at each strip is probably not the safest bet and you may need to call in a professional.