Question: I work in an office with 8 people.

We have no allocated seating. Which I am quite cool with. However, recently the tidiness has gotten quite out of hand. Papers, coffee stains, and some brochures scatter over the tables.

It's quite a rude shock when I almost put my laptop down on someone's old coffee stain in the morning.

Now my daily ritual is to wipe away all leftover hairs and dirt and choose an area that has less clutter.

We have introduced individual shelf compartment for us to store our personal goods. However, most of them still do not have the habit to clear up after themselves when they leave at the end of the work day.

I am quite concerned about how to keep the cleanliness, and would like to know if anyone has any experience in maintaining cleanliness in a free seating plan office?

Answer: 
The answer would be either:

1. To hire a cleaner
2. Have allocated desks
Those who refuse to return the space they are using for the day back to a neutral clean environment are likely doing so as a way to make the free seating arrangement painful. 

If all the work environments were equal in resources, space, and comfort; and the work required in the morning and the evening to convert those spaces to your use was trivial; then depending on the number of people vs work space involved, free seating might make sense. If there are 8 work spaces but 15 employees but many are at customer sites or on travel or working from home, then free seating is a way to better use the resources.

The behavior of those who continue to leave papers, stains and brochures at the end of each day may be a way of marking their territory. Or it a way resisting the lack of assigned seats. They may be leaving a level of clutter and filth that they can tolerate in the hopes that you won't take their seat. They may even settle for the situation where you spend time cleaning their spot from yesterday, while they take your clean spot.

The next phase of their plan is for somebody who likes a clean work space to complain to management and to try and put a cleaning policy in place....