I used grass gis v.surf.rst function to interpolate a surface using vector points. But it is very difficult to find a optimum parameters to be used. I am still unable to develop a accurate terrain
At first, as you did not tell, you want to create a raster form the points. A similar question about this can be found here: How can I create a DEM from Point Data? Second, I think there are tools in grass, callable from qgis, to make a depressionless dem, like the r.fill.dir tool. Other GIS-people tend to use saga gis functions, as described here: http://www.saga-gis.org/saga_module_doc/2.1.3/ta_preprocessor_4.html. For myself I always used arcgis functions from hydrology toolbox.