why clouds do not attract towards earths surface due to gravity?

Gravity or gravitation is a natural phenomenon by which all things are brought (or gravitate) towards one another - irrespective of size, i.e. stars, planets, galaxies and even light and sub-atomic particles. Gravity has an infinite range, and it cannot be absorbed, transformed, or shielded against. Gravity is responsible for the formation of structures within the universe (namely by creating spheres of hydrogen, igniting them with enough pressure to form stars and then grouping them together in to galaxies), as without gravity, the universe would be composed only of equally spaced particles. On Earth, gravity is commonly recognized in the form of weight where physical objects are harder to pick-up and carry the 'heavier' they are.

Gravity is the weakest of the four fundamental interactions of nature. The gravitational attraction is approximately 10⁻³⁸ times the strength of the strong force (i.e. gravity is 38 orders of magnitude weaker), 10⁻³⁶ times the strength of the electromagnetic force, and 10⁻²⁹ times the strength of the weak force. As a consequence, gravity has a negligible influence on the behavior of sub-atomic particles, and plays no role in determining the internal properties of everyday matter (but see quantum gravity). On the other hand, gravity is the dominant force at the macroscopic scale, that is the cause of the formation, shape, and trajectory (orbit) of astronomical bodies, including those of asteroids, comets, planets, stars, and galaxies. It is responsible for causing the Earth and the other planets to orbit the Sun; for causing the Moon to orbit the Earth; for the formation of tides; for natural convection, by which fluid flow occurs under the influence of a density gradient and gravity; for heating the interiors of forming stars and planets to very high temperatures; for solar system, galaxy, stellar formation and evolution; and for various other phenomena observed on Earth and throughout the universe.

The buoyant force due to air on clouds  is more than gravitational force , this is the reason!

the buoyant force acting on clouds by air has more magnitude compared to the weight of clouds. so clouds do not get pulled by earth due to gravity