To set predecessor options, open the Task Information dialog box and select the Predecessor tab. This task shows you how to create a task predecessor.
Creating a Task Predecessor
Double-click the task you want to edit.
Select the Predecessors tab on the Task Information dialog.
To create a new link, select the next blank row in the grid and select the task that should be linked from the drop-down list.
Select the Type value here for your link.
Enter a Lag value, if one is necessary.
Click OK to close the dialog and save your changes.
For Your Information
Make Sure to Save Your Changes
You must click the OK button on this dialog for the edits you have made to take effect. It is important to remember that if you edit a field on one tab, but then move to another tab, make more edits, and then click Cancel, that ALL the edits you have made in the entire dialog will be lost, not just the ones on the last tab you were on.