There is now a checkbox when you upload photos to make them available for sale directly. If you have not activated print sales, activate it by checking the checkbox "Enable sales" in "Account settings".
We are trying to increase sales in many different ways like partnerships with a number of companies which already sell a lot of prints and planned mobile apps. However, the most important strategy to increase sales is to make as many photos as possible available for sale. Buyers will be disappointed when finding out that their favorite images on 1x are not available. Therefore our goal is that all photos published on 1x should be availble for sale in the future, like in a real photo gallery. Go to "Account settings" > "Select photos to sell" to make your photos available for sale.
Make photos for sale automatically when you upload with the check box "For sale".