Don't forget though, Do-It-Yourself can save you money but if you're not committed to doing a good job, using quality products and preparing properly you could just be asking for more stress and most likely further costs. In this case we would always recommend using the professionals and paying good money for a job well done!
Any professional will tell you that preparation is the key. In fact up to 90% of the work is likely to be just that. First off before you do anything else make sure you have everything set out and easily reachable. Make sure you have plenty of light in the room and are wearing comfortable, old clothes. Anything you forget to do now will certainly crop up at the most inconvenient time (like atop a ladder). Don't scrimp on the setting up your room either. Make sure everything is moved away from the walls and properly protected with cloths or plastic.
Preparing the walls
It's always advisable to remove the old wallpaper first before putting up new. One reason is simply because by applying the new paper onto the old you will soak the old paper with glue causing wet patches. The patches will bring the old paper off the wall and it's these differences that will show through the new paper in the form of different textures and patches in the colour.
If you're not removing the old paper first and putting up light coloured wallpaper there shouldn't be any stains or colour differences on the old stuff. If there is you will need to paint it first. It's easy to assume that paper will hide any imperfections underneath but the key to a great finish is not to leave anything to chance.
To remove your old paper you need hot water and sponge and a wallpaper stripper. Add a little vinegar to the water for extra effectiveness. Apply the water to the paper and let it soak in for 10 minutes. It should now scrape off with little resistance.
The next thing is to ensure that the wall is smooth. Use sandpaper to take off slight rises and to score the wall, which gives the glue a proper grip. Use a soft brush to remove the dust when you have finished.
If you're pasting on to new or plastered walls you're going to want to paint them first with at least one coat of primer. This will ensure the surface is absorbent but also allow you to one day remove the wallpaper when you re-decorate.
The walls are ready, now for the really messy bit. The trick is to be ready. If you don't get the paper up in time the glue will dry too much and you won't be able to manoeuvre the paper, likewise, if you don't leave it to set for long enough the paper will slip.
The instructions on your paper will make this clear but there are two types when it comes to application. Non-woven backed paper requires that you paste onto the wall and paper backed means you paste on to the paper itself. When pasting directly on to the paper, if the glue has not set properly on to the paper the bubbles will not disappear. If you are using non-woven wallpaper you must remove any old paper first.
You generally want to start papering from the middle of the walls towards the corners. This is because you can never guarantee the corners are exactly straight which means your joins will not be either. Start by using a spirit level to lightly draw a vertical line the length of the central point of your largest or most prominent wall. Use this as a guide to place your first strip of paper. If your paper has reoccurring patterns you can also make horizontal guide marks so you can match these up easily too.
Bearing in mind you are working with wet paper which tears easily, make sure you are cutting with a very sharp knife. Going back to the earlier mention of preparation - make sure you have clean water and a towel at hand to quickly pick up spills or excess glue.
After you have glued your paper and are resting it while the glue readies (at this point you will have folded your paper to retain the moisture) gently roll from the two ends towards to centre. This will stop the edges of your paper curling and help stop them peeling when applied to the wall.
Avoid bubbles when pasting the walls by applying enough glue - if you find the glue is drying too quickly as you go - dilute some glue and cover the whole wall in advance - this will absorb into the wall and provide a less absorbent layer.
You will have some bubbles regardless of how much prep you have done. Do what you can to avoid them but for the most part these bubbles will disappear as the paper starts to dry.
The key to drying your new paper is to go slowly. You want the glue to dry as naturally as possible. You should keep all the doors and windows closed to avoid any drafts and excess moisture in the air and likewise don't force it by heating the room, however gently.
If you have bright coloured paper paint lines of same colour on to the wall around the areas where there will be a join in the paper - In case you have small gaps in your joins these will be hidden by the matching colour of the wall underneath.