One of the key ways to create realistic visual effects is through randomness of attributes. Setting appropriate ranges - so that every time the effect is played it looks different - also prevents the player from recognizing the repetition of visual effects as easily. Setting the lifetime of sparks, for example, between 0.5 and 1.5 seconds adds realistic randomness. Randomness can and should be applied to directional forces, scale and color. Wide ranges can lead to some extremely interesting results, so never be afraid to try adding random value ranges in any available setting.
Another method to avoid visual repetition within particle effects is to create particle textures with unusual shapes. The common technique used to create particle art is to generate a fuzzy circle of art, fading out the edges to avoid a hard edge in the game world. Experiment with making smoke clouds in a C shape or other random arc pattern. With a random starting rotation, smoke clouds will form more natural shapes and hide the visibility of individual particles that one sees with round particles.