As an owner or co-owner:
- Sign and register the tenancy agreement;
- Ask for a two-month rent guarantee (bank deposit or other);
- Ask the tenant for sufficient references (proof of solvency);
- Check that the monthly rent does not exceed 50% of the tenant's income.
If no tenant is yet occupying the premises, make sure you receive these documents as they will be requested if you ever report a non-payment or damage.