First option, wait for an invite to a private order from a photographer who likes your portfolio. You'll receive an invite via email and will be able to accept or decline an invitation.
Second option, participate in an open contest. Submit edited photos to a contest and work with the buyer if there are any comments. If your work gets selected you'll get funds deposited to your account in accordance with the contest budget and expect a follow up private order.
Although, there is no obligations for a buyer to submit more work for you but this is likely going to happen especially if open contest description had a reference to the long-term conditions.