First you must edit your form and under the "form processing" tab - set the "spoof check" option to "no"
Then you can build your link as follows:
Code:
index.php?option=com_fabrik&task=form.process&formid=1
replace the 1 in "formid=1" with your form id.
Then for each field you want to insert data into add '&tablename___elementname=value'
e.g.
Thus, for my example form my final 'add' link will look like this:
HTML:
<a href="index.php?option=com_fabrik&task=form.process&formid=1&contacts___name=rob">Add a contact</a>