We have worked out the structure of optical spatial solitons in liquid crystals. The optical nonlinearity in these systems can be due to (i) Director reorientation, (ii) Suppression of the director fluctuations, (iii) Change of tilt angle in smectic liquid crystals, and (iv) Thermal indexing. When we considered the combined effect of laser suppression of the director fluctuation and thermal indexing we not only get the usual soliton solutions but also find a kink soliton solution. When both the third and fourth processes are operating we find a soliton solution with the nonlinearity which can continuously change from one type to the other. We have worked out the critical laser power required for the formation of solutions in different cases. We have also addressed ourselves to nonlinear optical effects on light propagation in liquid crystals, In the case of beams with large width for which diffraction can be ignored we find interesting modulation of the beam width in a nematic due to the second and fourth processes.