If you want to save money on your home renovations, painting rooms yourself is one of the easiest ways to do it. Having painters come in for a day will generally cost you at least a couple hundred dollars in labor when you could quite easily paint it yourself.
The part where most people get confused is just learning all the steps you should perform when painting. The act of painting itself is pretty straight forward, and any old chimp could become an expert pretty quickly. I've included these simple steps in the following step by step guide:
The first step is to give your walls a light sanding so the paint will have a better texture to stick to. Once you've sanded, wash the walls with a TSP solution.
At this point you will want to lay down either some drop clothes, tarps or newspapers to protect the flooring. Don't be lazy, protect your floors, if you spill paint on them, the cost of repairs will far outweigh the savings from painting yourself!
Ideally, you should probably prime your walls prior to painting, although it is not 100% necessary if your walls are in good condition, if you are using the same type of paint, or if you aren't drastically changing the color. If the existing paint is latex or oil based and you plan on not using the same type of paint, you will need to apply a coat of water based primer to ensure your paint will bond to the wall. If you apply latex paint over an oil based paint(or vice versa), your paint will not properly bond and will deteriorate. You will also want to apply a coat of primer if your walls have no paint yet, if the existing paint is dark or if you plan on using a lot of tape on edging.
Once you've primed you now have a couple options in regards to edging the room. Edging or cutting is a term used when painting an area next to another surface you don't want to get paint on. You can either use an edging tool or a drywall taping knife if you are too lazy to use tape. If you do decide to use tape, tape off around doorway moldings, tape along the roof line and don't forget to remove the face plates from all electrical outlets and switches. When using tape to protect the other surfaces, make sure you prime the walls before hand or you risk pulling the fresh paint off the wall when you remove your tape.
The next step is going to be painting the walls themselves! There are many different techniques you can use, but the most popular is the "W" technique. Basically, you take a section of the wall roughly 2 feet by 2 feet and roll the paint roller in the form of a W and keep going over it until the entire region is covered in paint. You repeat this technique until you have rolled paint over the entire surface wall. Give the paint 24 hours to dry and then apply a second coat.
After you've applied your first coat of paint, you should begin edging/cutting; you will want to apply two coats when edging as well. To edge, get an angled brush and slowly go around the edges, (where you hopefully taped), and carefully apply paint while trying to get as little paint as possible on the other surfaces. This is probably the hardest piece of the entire process. You will want to keep a wet rag handy in order to clean up any paint you get on the room or moldings.
If you also want to paint the roof, make sure you paint it prior to painting the walls as chances are you will splatter white paint all over your freshly painted walls. Before painting the roof you will want to wash it with TSP and apply water based primer since it is hard to gauge what king of paint was previously used on the roof.
That is pretty much it, just remember to be patient especially when it comes to cutting/edging. Your edging skills may take a few tries to really master, but if you tape your walls before hand you shouldn't have to worry too much!