Scrape away any peeling paint or loose material from the wall.
Fill in any holes, cracks or gaps in the wall using the drywall knife and plaster. Make the patch as flat and solid as you can. Let the plaster set for 12 hours.
Spread plaster over a few square feet at one of of the wall with the wide drywall knife. Apply it to a depth of about 1/4 inch.
Press a grout float into the plaster so the whole flat edge of the float sits flush to the wall. Pull the trowel straight outward, creating peaks and ridges.
Set the float back into the plaster, next to the previously textured spot. Pull it out again to create a second area with texture.
Repeat the process, pressing and pulling at the plaster until the entire area has texture.
Spread a second section of plaster next to the first. Texture the whole section as before, making sure the first and second sections are completely melded together by the texturing.
Continue across the whole wall, spreading and texturing the plaster section by section. Let it dry for 24 hours before painting it.