Hatching and stippling: these two techniques allow you to create strikingly gradated, very "pro" effects!
Note: Hatching with acrylic paint is a delicate method that requires a lot of precision: be patient and keep practicing... Your efforts will be rewarded!
For an easy way to create fine, parallel lines in color, use an old toothbrush with long, stiff bristles instead of your paintbrush.
Note: this technique can damage your paintbrush.
Painting just with dots really can be done! Go ahead and soak up some inspiration from the works of Georges Seurat, one of pointillism's great masters.