I just had a quick runaround in your map, And noticed a few textures we're not only out of scale but unaligned as well, And door textures are sticking out when open, As well as the flaws kraid has pointed out.
But this is normal of course, It's your first time playing around hammer and it takes time getting used to, Everyone has to start somewhere. Let me give you a few starter tips.
-I suggest you use this current map as a test file, So you learn the ropes around as you play with this, Then when you think you've acquired sufficient knowledge, Start a new map from scratch and use all your knowledge into building it.
-Make your doors smaller, They seem to be about 40 units thick, That's pretty big, And it's the same size than the wall, Thus making the texture stick out as I pointed out earlier, Try to proportionate doors with the scale of the walls more appropriately.
-Use light_spot entities over simple 'light' entities, They are much less overly bright are give an overall better feeling.
-Do a small room outside the map with differently sized brushes and play around the texture tool so you get a hang of it, And while you're at it, Play around with lighting/shadows and the lightmap scale.
-Focus on smaller brushes as well so your map doesn't look too "Cubical".
-Use env_cubemap entities all around your map.
-Learn about prop placement, I'd say start off with lamps and wall lights, So your main lighting doesn't come out of nowhere.