You will need a few clean linen or lint-free cotton cloths or rags. Decide which method you want to use: rolling on or rolling off. Each of them provides different variations of the same texture. Rolling off usually means less of the base coat will show through, compared to rolling on the paint. Rolling off also usually requires more rags because they eventually become saturated with paint and cease to provide the desired effect. Choose a small portion of the wall to use as a test area to see which method works best for you. You can always paint over what you've done.
For the next coat, use a slightly darker shade of the same color paint you used as your base coat or vice versa, if you want the base coat to be darker than the top coat.
For better results, try diluting the paint for the next coat by mixing it with water in a paint tray. Aim for getting the mixture at a ratio of 2:1 (paint to water).
If you're rolling on the paint, dip your rag into a paint tray to cover it with paint. Be careful not to over-saturate the cloth. Twist it or bunch it up into a ball to distribute paint evenly throughout and then roll the cloth down the wall with steady pressure, starting at the top. Try not to use the same downward stroke each time or the results may be too uniform; you want to use slightly angled, different strokes, re-adjusting as you move along the wall. Keep extra rags handy, as once one becomes too saturated with paint, you'll need a new one because it won't work in the same way. Do this across the entire surface of the wall until you've covered it completely.
When rolling off the paint, apply the next coat of paint over the base coat with a roller or paintbrush. Then, immediately begin rolling a clean twisted or bunched up rag down the wall. The clean rag will pick up paint from where you just painted, creating the textured appearance.
Do small areas at a time so that the top coat doesn't dry before you begin rolling.
Once the rag has become completely saturated with paint, discard it and use another. Keep applying paint and rolling it off in downward strokes across the surface of the wall until you've covered it.