There are a few different ways that this sentence could be reworked in order to make it flow more smoothly. Of course, when editing any writing, it is import to think about the intended meaning of the sentence. Grammar can help writers make their messages to their readers so much more clear!
Let's look at a few options.
One of the first things I notice about the sentence is that there seem to be two different clauses.
"Look through the window" and "You can see the city lights at night"
The issue seems to be that they are not correctly connected. In order to connect two clauses, we can use a period, a comma and a conjunction, a semicolon or a subordinate clause. There are many ways to connect two related clauses, so try playing around with these options to see which one reads the most naturally for you.
"Look through the window. You can see the city lights at night."
This is grammatically correct, but it reads in a way that is a bit disjointed. Try to connect the two clauses in a way that connects them more closely.