The Parthenon within the Acropolis is undoubtedly the most famous and iconic section of Athens, which means it fills with tourists daily. We found one way to avoid the crowds at least for a little bit.
The ticket office of the Acropolis is located about 30 feet from the main entrance and opens at 8:00 AM, a few minutes before the Acropolis gates open. To get inside the complex before the crowds,here are the key steps to follow:

1. SHOW UP AT THE TICKET OFFICE NO LATER THAN 7:30 AND STAND AT THE TOP OF THE STAIRS -By 7:45, tour groups and other people will have arrived, a line might form but don’t be shy and be aggressive, if you were one of the first people there, stay in front by the ticket windows. When they open have your cash ready, it’s 20 Euros per person (it’s much faster to pay with cash).  

2. WHEN YOU HAVE YOUR TICKET IMMEDIATELY WALK TO THE ENTRANCE GATE ON THE OTHER SIDE OF THE TICKET WINDOW -When we were there, the gates opened about 1 minute after we got our ticket and we were the third people in after the gates opened.

3. WALK FAST UP THE HILL TO THE END OF THE ACROPOLIS TO THE PARTHENON -Don’t Stop for Pictures along the Way! Most people and all tour groups will get distracted and take pictures along the way. It’s not the best part and not worth it. This is what slows the crowds and allows the complex to stay relatively empty till 8:30. It’s a relatively steep climb but if you are reasonably fit and motivated, you will get up quickly without a problem.

We raced past these stairs to get to the Parthenon and revisited on our way out

4. ENJOY YOURSELF. THIS IS ONE OF THE GREATEST HISTORICAL SITES IN THE WORLD! – Being there early you’ll be able to enjoy the great history and sites without the crowds and will also see the Greek military’s flag raising procession. When you exit you’ll be amazed by the crowds on the way down, and all the people who chose to take pictures on the climb to the Parthenon.

The flag raising ceremony by the military happens shortly after 8, another reason to rush towards the Parthenon

5. Don’t forget about the North Slope. We essentially enjoyed the Acropolis in reverse order, rushing to the Parthenon and the Temple Athena at the onset and then exploring the hill entrance on our departure. As we were preparing to exit we found a walk way to the North Slope walk which is at the base of the Acropolis entrance. All the tour groups were so focused on reaching the Parthenon it was empty. We were able to explore this area in seclusion wrapping up our lovely Acropolis morning here.  
Here are some photos from the secluded and often overlooked North Slope:

Finally since you’re planning to get up early anyways- why not take in the sunrise? 

Just below the Acropolis is the the Aries Pagos Hill, it’s about 100 feet away from the ticket office. We arrived around 6:30 with pastries from a local bakery an enjoyed a beautiful sunrise over Athens.