First things first, log into Airtable. You can either start fresh with a new base or open one you already have. This is where we'll set up our data validation.

Head over to the table where you want to add some data validation. Click on the field (or column) where you want to set up the rules.

Click on the header of the field you picked. A dropdown menu will pop up. Select the “Customize field type" option from there.

Make sure the field type matches the kind of data validation you need. Common ones are Single line text, Number, Single select, Multiple select, and Date.

Set up the specific properties for the field:

• For Single line text, you can set patterns or length limits.
• For Number, you can specify decimal places, or set a min and max range.
• For Single and Multiple select, define the options users can pick from.
• For Date, choose the date format or restrict to future/past dates.

For more complex validations, you can use a formula field.

• Create a new field of type "Formula".
• Write a formula that returns true for valid data. For example, IF(LEN({Field Name}) = 10, "Valid", "Invalid") checks for exact text length.
• Use this field to flag rows with invalid data.

Create filtered views or conditional filters to show only the rows that meet your validation rules. This helps you quickly spot any invalid data.

Set default values for fields to make sure data entry starts off on the right foot.

Mark the field as "Required" to make sure it's always filled out during data entry. You can do this in the field customization dialog box.

Connect Airtable with other tools through Zapier, Integromat, or Airtable’s scripting block to enforce more advanced validation rules.

Regularly review and audit the data in the table to make sure it keeps following the validation rules. Use views and reports to manage this efficiently.