There are no restrictions on how you might choose to share your space - however there are a number of issues that you might want to consider when making arrangements to share your gardening space with another member of your community.
For starters, you should treat making your first arrangements with your prospective yard-sharing partner the same way you'd look for a tenant or a roommate. First speak to them over the phone -- do they sound like people you'd like to meet? Then meet for the first time in a public place, like a coffee shop or public library. You might want to bring a friend along.
If you decide this person is someone you'd like to share your yard space with, you can review the following considerations with them. Be thorough and creative! Think of other aspects you can discuss as well.
Seeds / Transplants
Privacy and Security Considerations