My girlfriend lives in Ghana. I want to get her to the United States. What steps do we need to do to expedite this trip?

I will assume this is a real girlfriend, someone you meet when you visted that county, not someone you meet over email, that wanted you to send them money for a passport, then money for a visa and more.
Ghana has a large business in fraud, having girls pretend to be coming to the US and cheat men here out of 1000' of dollars.
You can contact the US embassy in Ghana ( who has pages of warning about dating scams) and find out more.

I agree with "Fr_Chuck" remarks about dating scams,

But say if you a US citizen and really want to bring her to the US, then marry her and bring her on a spouse visa.

Otherwise she can come herself temporarily on a visitor or work visa (like H1, H2 etc.. ).

Your girlfriend, have you visited her within Ghana inside the last two years AND taken pics of you two together? Such is a serious starting point in the US Embassy's eyes.
Go over to VisaJourney - Your US Immigration Community and get the direct particulars on your case.

Best wishes

PS: As an Afr Amer male, I have been to Ghana many times and too been to its US Embassy there.