Begin by ensuring that both your Oracle Database and Microsoft SQL Server environments are properly configured and accessible. Install the necessary Oracle client tools (like SQL*Plus) and ensure you have access to SQL Server Management Studio (SSMS). Verify that you have the necessary permissions to read data from Oracle and write to SQL Server.

Use Oracle's SQL*Plus or another Oracle client tool to export the required data. You can utilize the `SQL*Plus` command to spool data to a CSV file. For example:
```sql
SET HEADING OFF;
SET FEEDBACK OFF;
SET LINESIZE 1000;
SET PAGESIZE 0;
SPOOL your_data.csv;
SELECT * FROM your_table;
SPOOL OFF;
```
Adjust the SQL query to match the specific data you need to export. Ensure the output is in a format that is easily importable into SQL Server.

Once you have the data exported to a CSV file, open it in a text editor or spreadsheet application to ensure that the data is correctly formatted. Rectify any issues such as incorrect delimiters or data type mismatches. Save the CSV file once you are satisfied that the data is correct.

Using SQL Server Management Studio (SSMS), create a table that matches the structure of your Oracle source table. Ensure that data types are compatible and that the table schema can accommodate all the data from the Oracle export. For instance:
```sql
CREATE TABLE your_table (
column1 INT,
column2 VARCHAR(255),
column3 DATE
-- Add additional columns as necessary
);
```

Use the SQL Server Import and Export Wizard, which can be accessed from SSMS. Choose the 'Flat File Source' option and specify your CSV file. Configure the destination as your newly created SQL Server table. Map columns appropriately, ensuring data types match between the source and destination.

After importing the data, perform checks to ensure all records have been transferred correctly. Run SQL queries to count records, compare key fields, or perform checksum operations to validate data integrity between the Oracle source and the SQL Server destination.

Once data integrity is confirmed, consider creating indexes on important columns in SQL Server to optimize query performance. Additionally, you might want to clean up exported files and document the process for future migrations. Ensure backups of both databases are up-to-date before making any final changes.
By following these steps, you can successfully migrate data from an Oracle Database to Microsoft SQL Server without relying on third-party connectors or integrations.