There are as many techniques for painting as there are artists. Artists are constantly developing new ways of doing things in order to achieve a specific effect or as experimentation. For example, the Abstract Expressionists broke European tradition in the 1940s with their use of materials and process—using house paints and house painting brushes, and pouring, flinging, and dripping paint. The Metropolitan Museum of Art Heilbrunn Timeline of Art History says about Abstract Expressionists:
"Breaking away from accepted conventions in both technique and subject matter, the artists made monumentally scaled works that stood as reflections of their individual psyches—and in doing so, attempted to tap into universal inner sources. These artists valued spontaneity and improvisation, and they accorded the highest importance to process."
Abstract Expressionist Jackson Pollock is most well-known for his large-scale "all-over" paintings that he painted by laying raw canvases on the floor and pouring house paint directly from cans or dripping it from sticks while engaged in almost dance-like rhythmical movement around the canvas.
Traditionally an artist paints with brushes and perhaps palette knives on a primed canvas, but many will also use their fingers and hands, some their feet, and fewer still, other body parts. Some artists even incorporate their whole body, or someone else's, into the painting. Some use other than traditional art tools to make a mark or move paint around on a surface. Some experiment in using paint in unexpected and unusual ways such as throwing, pouring, flinging, spraying, and blowing it onto and around a surface. Some even spit and regurgitate paint (not something I recommend). And many techniques that were once experimental have now become common as new art supplies and tools are introduced to the market and artists share ideas and techniques.
Current examples of unusual painting techniques that might inspire you to push your own boundaries:
Although it is important and helpful to learn how paint materials and techniques are traditionally used, don't be afraid to experiment. The ways to create a painting are limitless.