1) good quality paint brushes. Get at least one angled sash brush 1-2" wide for trim
2) paint edger and refill pads
3) painters' tape (not masking tape)
4) paint rollers and a paint roller frame - select the right nap for your walls
5) an extension pole for the frame
6) paint trays - metal or plastic.
7) drop cloths
8) Putty knife - I love the 5-in-one tool which has multiple uses in a painting project
9) Spackle compound to fill holes and cracks - or a tube of painters nail hole filler
10) Sandpaper to smooth
11) Caulk and caulk gun to fill cracks between trim and walls
12) Wall cleaner like TSP - tri-sodium phosphate
Some shortcuts you can use:
If you have metal trays, you can use plastic liners and your tray stays clean. I don't recommend throwing liners away since it's not necessary to add to a landfill, so get the recyclable ones and rinse off the paint.
Paint rollers and brushes can also be stored with paint on them as long as they are completed sealed in an airtight plastic bag in the refrigerator or freezer.
Control paint splatter with a paint roller shield. The right nap roller also resolves this issue.They simply snap onto the roller frame and partially cover the roller.
Preparation is a necessity that will make the overall project much easier and the results better. Place drop cloths on floors and furniture. I love fabric cloths since they can be re-used nearly endlessly, and don't waste plastic or paper; I wash mine periodically and they have been a great investment for many other uses. Remove outlet and switch plate covers in the room. Use a clear zipper storage bag or lay them out on newspaper; I almost always paint them the wall color. If the walls are very greasy or dirty, use TSP - with rubber gloves - and wash the walls following the manufacturer's directions. Rinse the walls with clear water. When the walls are dry and then it's time to tape, patch and prime as needed. If the new paint color is a stark contrast to the old paint you will use fewer coats of paint if you put on a coat of primer first. Have your paint store tint the standard white primer for you to make it closer to your paint color. The walls will also need a coat of primer if your paint type is changing from a oil-based paint to latex (water-based) paint. If there are severe stains on the walls, a stain blocking primer like KILZ will be your best friend. No matter how many coats of paint that are put on the wall, many stains will continue bleeding through the paint unless a primer is applied. Tape off trim, windows, and other areas that will not be painted. Use blue tape meant for easy removal; masking tape is NOT the right product.
I start by making sure my paint is mixed well. I open windows for ventilation, although I highly recommend low odor and NO or LOW VOC (volatile organic compound) paints to eliminate or minimize any chemical off-gassing. Then I pour paint for rollers into paint trays, and into a small bucket for cutting in. Cutting is is simply painting the areas that cannot be reached with the roller, such as next to the ceiling, trim and in the corners. I do it first since I find that I can 'smooth' the edges by rolling over them. You don't need to cut in a wide area, just enough to fill where the roller cannot reach. Use a trim brush or the flat pad for that.
When you're ready to start the walls, start rolling your roller back and forth on the ridged area of the paint tray to evenly distribute the paint on the roller. The roller should be thoroughly covered but not dripping with paint. Begin rolling the paint on the highest part of the wall in a "W" or "M" design and then keep rolling until the area is evenly filled in and the paint is distributed. I go all the way to my 'cut in' line for even coverage on the wall. This process will be repeated each time the roller needs to be refilled with paint. Usually an area approximately 4' x 4' can be covered with each roller refill. Begin each new "W" beside the previous and then blend the paint edges together while still wet.
You will be pleasantly surprised how quickly a room can be completely. Allow the first coat of paint to dry for about three hours before applying the second coat of paint. The drying time for the paint will depend on the temperature and humidity. As the paint begins to dry, it will be much easier to see any areas that haven't been covered completely and it will be easier to determine how many coats of paint are needed.
Be sure to wait until the paint is dry before removing the drop cloths. Be cautious when removing the paper's tape as well. Good quality paint brushes and rollers are an investment worth taking care of and they will need to be washed thoroughly when the paint job is complete. There are special tools available to even help with the cleaning process of rollers and brushes. It's always a good idea to allow the paint at least a full day to dry before hanging pictures back on the walls.