Begin by manually exporting the data you need from Wrike. Login to your Wrike account, navigate to the relevant project or task folder, and use the export feature to download data in a compatible format such as CSV or Excel. Ensure that the exported data contains all necessary fields and is saved locally on your computer.

Open the exported file and review the data to ensure that it is clean and formatted correctly. Remove any unnecessary columns or rows, and verify that the data types (e.g., strings, integers, dates) are consistent with those in your PostgreSQL database schema. Save the cleaned file, preferably as a CSV, for easy import.

Ensure that your PostgreSQL server is running and accessible. If not already installed, download and install PostgreSQL from the official website. Set up a new database or use an existing one where you intend to import the Wrike data. Make sure you have the necessary permissions to create tables and insert data.

Use SQL commands to create a table in your PostgreSQL database that matches the structure of your cleaned CSV file. Connect to your PostgreSQL database using a terminal or a graphical client like pgAdmin, and execute the `CREATE TABLE` command with appropriate column definitions and data types.

Use the `COPY` command in PostgreSQL to import the cleaned CSV file into the newly created table. This command allows you to efficiently load large datasets directly from a file. Run the following command in your PostgreSQL interface:
```
COPY your_table_name (column1, column2, ...)
FROM '/path/to/your/exported_file.csv'
DELIMITER ','
CSV HEADER;
```
Replace `your_table_name` with your actual table name and adjust the column names and file path as necessary.

After the data is loaded, perform checks to ensure that the import was successful. Use SQL queries to count rows, check for null values, and verify data types. Compare a sample of the data in PostgreSQL with the original data in Wrike to confirm accuracy and completeness.

For ongoing data transfers, consider writing a script using a programming language like Python. The script can automate data export from Wrike via their API, clean the data, and import it into PostgreSQL using similar steps. Schedule the script to run at desired intervals using cron jobs (Linux) or Task Scheduler (Windows) to keep your database updated with minimal manual intervention.

By following these steps, you can efficiently transfer data from Wrike to a PostgreSQL database while maintaining control over the process without relying on third-party tools.