Optional - On the setup page, you can select a time frame to restrict whether older campaigns should show up in the Campaign Influence related list on an opportunity – after all, you may not want an email from last year to get credit for an opportunity closed yesterday.

If you enable a time frame, the best practice is to align it to your sales cycle. If you have a short sales cycle, then create a relatively short Campaign Influence time frame. For example, if your sales cycle is only 30 days from creation of the opportunity to closing the deal, you might want a 60 day Campaign Influence time frame. However, if your sales cycle slows down along with the economy, this may incorrectly remove influential campaigns, so use your best judgment here.

Note: This filter affects which Campaigns appear in the Campaigns with Influenced Opportunities report.

Optional - You may want to further filter which campaigns appear on the opportunity. Perhaps you only want to see active, in-progress campaigns, or you do not want to see partner campaigns. Under Create Association Rules, you can add the filters to show only the campaigns you want.

Note: These filters affect to the Campaigns with Influenced Opportunities report. Also, note that Primary Campaign Source on the Opportunity is not impacted by Campaign Influence. The last associated campaign with a converted lead will always be the default Primary Campaign Source and included in the Campaign Influence related list unless it is changed on the Opportunity.

Once you’re done enabling Campaign Influence and configuring the optional settings, click Save.

(2) Add the Campaign Influence related list to the opportunity page layout

To add the Campaign Influence related list to the opportunity page layout, click on Setup>>Opportunities>> Page Layouts and click Edit for the layout you want to modify.

Next, click on Related Lists and drag the Campaign Influence related list into the page layout canvas.

Once you’ve positioned the related list (pictured below) in the order you want,  click Save and you're done for this layout!  If you have multiple Opportunity page layouts, repeat adding the related list to ensure Campaign Influence shows up for all page layouts you desire.