How Can I Have Subscribers Start On a Certain Follow Up Message?

If you want your subscribers to start on a certain message in your follow up series, you can easily modify your web form to do this.

Step By Step Instructions

Either create a new form or open an existing one by going to the Web Forms page, then clicking the name of the form in question.
When working on the web form, click the Settings tab.
Here, click on "Show Advanced Settings".
Choose the message you would like your subscribers to start on from the "Start On Message" dropdown.

Note that the last option in this drop down menu is "No Followups, only Broadcasts." You can choose this to have subscribers skip the follow up sequence for this list entirely, but still get broadcast messages sent to the list as normal.
Now just hit to save your form, and publish the form as normal.