Anybody can paint a wall. The trick is to do it efficiently. It is the cheapest and quickest way to update your decor, or just try to make it presentable. In fact, sometimes it is just easier to paint then to clean. If your landlord's a stickler and there's stains on the walls from that party last month, just spot coating them won't get your deposit back...you're gonna havta paint the whole wall.

There are 2 methods of painting,- the official"RIGHT" way, which you should always use if you own your place, or are planning to stay for more than a year. There is also the "CHEATERS" way which is perfectly appropriate for dorms, squats, stage, and cheap apartments. Both ways look similar, but the proper way is smoother, lasts longer and will save you maintenance in the future. In this Instructable I am putting in all the proper steps and will put in italics any parts that could be skipped if you're in a cutting corners mood.

Step 1: Choosing Your Paint

How much do you need? One gallon of average quality paint will do one coat on approximately 400 square feet.
Here are two links that can help you find out how much paint to buy.
benjaminmoore.com
paintquality.com
What finish do you need? A shiny finish is easier to clean dirt off of, but will show more imperfections. A flat (or non shiny finish) will cover up wall problems better, but is hard to get clean. The average wall is painted with an eggshell finish, sorta in the middle. Woodwork is commonly painted with a high gloss, which is very shiny. From flattest to shiniest the types are: flat, eggshell, satin, semigloss, high gloss, and enamel.
Primer? Quality? If you are making a color change you will need several coats of paint. A higher quality paint will cover better, meaning less coats. Primer is useful as a first coat when you are making a severe color change. It comes in white but can be tinted. Primer is also a good idea if your wall is in bad shape to help your paint adhere and last longer.
What type of paint? For indoor walls, there is no reason to use oil base paints. water based paint, i.e. latex or acrylic is fine. They are now marketing "greener" versions, that claim lower odor and better for environment . I have been told they don't work as well, as well as costing more. A more environtmentally concsious choice is to acquire "recycled paint" from your local Restore, or recycle outlets.

Step 2: Assemble Your Equipment and Supplies

You will need:

1 gallon of paint for every 400 sq. ft.
the same amount of primer if drastically changing colors
1 roller and pan
edge brush OR an edge roller pad OR a small regular brush
painters masking tape
scraper OR metal spatula
wash rags
stuff to protect the floor and furniture and YOU
paper plates
1 big nail
sand paper
tri-sodium phosphate OR spic and span OR vinegar and baking soda (this is for cleaning the wall, tri-sodium phosphate is used to degrease and abate lead. Lead was used in paint until the 1970s, so if you sand a wall that was around then, you should clean up very well. VERY WELL. )
tack cloth (this is a disposable sticky dry cloth that which is the first step of cleaning up , you could substitute a damp rag or paper towel which you should throw away.

Step 3: Get Ready

Tape paper plate to bottom of can. This will catch any drips.
Pry open can, hammer large nail to make holes in lip of can every few inches as shown. This is so the paint will run back into the can. Replace cover.
Move or cover everything in the room.
Cover up the kids in big old stuff and cover or put your hair up.
Lock the cat in the bathroom.

Step 4: Prep the Surfaces

Preparing your surface well is what makes a quality job that lasts. If your wall is in good shape all you will need to do is clean it. Wash it down with a rag and cleaner of your choice.
However most walls are not in good shape, often meaning your prep will take longer than the painting. If there are holes or cracks they should be repaired, but that's another Instructable.
If there are any places where the paint is peeling, scrape all loose paint off, then sand to smooth the edges. Remember, the difference between the bare wall and the old paint will show up as lines if you don't . Also sand any places where there are raised surfaces, such as spackle, crayon , tape residue etc.
After sanding, use your tack cloth to wipe down the surface. Then wash all surfaces, preferably with the tri-sodium phosphate.

Step 5: Gettin' Edgy

Make sure the cat is still locked in the bathroom. Open the can. Using your edge brush, paint a band about 2 inches wide around all the edges of the wall and around any doors or windows. This is called "cutting in". In order to get a neat line where the wall meets woodwork or a wall of another color, there are several different methods. Most beginners find using painters masking tape easy. This blue tape is pressed along the edge you are trying to protect, then you just brush along it. When the paint is dry, peel off the tape. I find that the pain can easily leak under the tape, thus not giving a perfect result. Additionally I think it is a waste of money and resources to through out something after only using it once. Another method is to buy a foam pad edger kit and follow the instructions. The final method takes practice but gives superior results. This is to use and edge brush ( a slanted specialty brush) or a small and soft paint brush. You dip the brush into the paint, allowing more than the usual amount to remain on it. This is called "loading" the brush. You then very carefully and slowly pull the brush along the edge. Allowing the excess paint to make a smooth line as you pull the brush down. Learning how much paint to load the brush with so it won't drip, is as important as learning how to push the bead of paint along in a straight line. Practice makes perfect. And a good way to practice is to put on the painters tape and then use the loaded brush method. By the time you finish your first wall, you'll probably be very good at it.

Step 6: It's Time to Roll

Pour a little paint into the pan. About an inch at the most. Dip your roller in the pool of paint and then roll your roller up and down the inclined portion of the pan. This is to get the paint to spread evenly over the roller. You'll notice if you have to much paint on your roller it will just smear and slide. Too much paint can also cause a lot of spatter. You would look pretty funny with purple freckles! Start by rolling a "w" on the wall then work back and forth to spread the paint. Keep reloading and rolling until you fill in the rest of the wall. NOTE: you could also reverse the order of edging and filling in, if that would be better for your project.

Step 7: TADA!

When your finished you will make the painting faerie happy if you clean up properly.
If your project is complete and you still have a fair amount of paint leftover, be sure to store the paint so you can reuse it. For best results, cover the opening of the paint can with plastic wrap and securely seal the lid by taping around the edge with a hammer. When you are sure the lid is leak-proof, turn the can upside down and store it at room temperature to avoid freezing.
If you need to get rid of extra paint and there is not a leftover paint collection or recycling program in your area, let your latex paint air dry away from children and pets. A small amount of paint in the bottom of a paint can is easily dried out by leaving the lid off. Once the paint is hard, discard the paint can with the lid off. Larger volumes of latex paint can be dried in a box with absorbent material such as shredded paper or kitty litter. Recycle the empty can with the lid off and dispose of the dried out latex paint as garbage. If the paint in the can is solidified all the way through, it may be disposed of as garbage with the lid off to prevent the build up of pressure in the can.
OH yeah, It,s time to let the cat out of the bathroom and give it a treat.