Adding a Precondition 
In the rule editor you can set rules as preconditions to another rule. When you set a precondition, the existing rule gets fired only when the precondition is satisfied.
Procedure
Locate the ruleset (Where is my ruleset?) and double-click the ruleset node.
In the Outline view, choose a rule node.
In the rule editor that appears, under the Preconditions section, choose the Add icon and choose a rule in the drop down menu.
By default the rule is set to must be satisfied. You can change it to must not be satisfied by clicking it.
Save the changes.
Note
To delete a precondition:
In the rule editor that appears, under the Preconditions section, select the preconditions you want to delete and press Ctrl + D.
In the dialog box that appears, select the preconditions you want to remove and choose OK.
You can choose the Select All and Deselect All buttons to select or deselect all the conditions all at once.