You may want to use tools other than the line tool. Although it is very neat, it doesn't really take much. Try using tones of grey to color them and define shadow. Also, try using different shades of blue in the sky. Look at other pictures and try and figure out what makes them look good and try to apply it to your picture. I myself am not amazing, but you can memo me for help.
drawn in 28 min
I like the city its cool.
drawn in 28 min
drawn in 24 min