Lay down a layer of old newspaper over the floor of the room you are painting to prevent any paint from dripping on finished surfaces. Remove any furniture or cover with drop cloths.
Repair any imperfections in the walls by closely examining them and filling any problem areas with hole filler (for example, polyfilla) using a putty knife. Allow the filler to dry before sanding it smooth to the surface of the wall.
Tape off the border of the wall you wish to paint. Ensure the edge of the tape closest to the wall you will paint is securely taped to the adjoining surface. You may also want to tape the newspaper on the floor to the wall to prevent it from moving away from the wall, creating a potential spill area. Do not forget to also tape the ceiling surfaces closest to the wall you are painting, as well. At this time, you should also remove any electrical outlet or light switch covers and tape the exposed elements.
Mix your paint with the included mixing stick. You should do this even if the paint was just mixed by the shop at which you purchased it. Pour some paint into your tray, and you are ready to begin.
Using a regular brush, paint the edges you have just taped off that will not be able to be reached with the roller. Ensure an even coat is applied and that there is enough paint on the brush to lay down a layer with minimal brush strokes visible.
Apply some paint onto your roller by rolling it in your paint tray. Apply the paint to the wall in a vertical pattern, meeting the brushed-on trim you applied in Step 5. Try not to get too much paint on the roller or roll the paint on the wall too quickly, as this can cause paint to spin off it and splatter.
Repeat Steps 5 and 6 until there are no more thin spots on your painted wall. Wait a few hours between coats to let the paint dry before checking for any thin spots.