You should be aware that such an extensions with doch is not necessarily positive. Be aware that I'm from Austria, so that might be a small cultural difference here to somewhere else or only my personal experience/view. Consider the following example:
Es zieht und mir ist kalt!
It's cold and there's a terrible draft!
There are now two responses:
Dann mach das Fenster zu.
Then close the window.
This is an appraisal and a suggestion.
Dann mach doch das Fenster zu.
Well, (already) close the window already.
I'm not sure about this translation, so please let me explain. The doch in this context, together with an irritated and/or uninterested tone, can have the meaning of "why do you bother me with this if you can fix it yourself?". Similar example:
Dann mach was du willst!
Dann mach doch was du willst!
At least for me the doch adds a sense of "if you ain't gonna listen to me then leave me alone" in this context and adds a slightly offended tone to it. Be aware that this is extremely based on context and tone of the voice.
Make sure to check out all the examples on the german Wiktionary page on doch.