you can check if the coregistration was sucessful by creating an RGB of both intensities as described here: Fault marking by InSAR Data and difference between SLC_1SSV and SLC_1SDV?
Is there a reason why you selected exactly these two dates? For a more stable phase and higher coherence, you should aim for images with smaller temporal baseline. Also the perpendicular baseline plays a role. Have a look at this document http://www.esa.int/esapub/tm/tm19/TM-19_ptB.pdf
Section 1.3 Selecting images for InSAR DEM generation