Thanks to GSP’s targeting options you have the ability to add competitors names (and even their domains) to your keyword list as part of Domain targeting. The GSP’s handle the rest by targeting Gmail users who have searched for (or receive mail from) those brands and Gmail users who actively mention those brand names in their mail.
Begin by compiling a list of as many top-performing competitors in organic searches, and their domains if possible, then add them to your display keyword list during or even after setting up your GSP campaign under the “Display Keywords” section which you can find under the “Display Network” tab (as shown in the example below
This is just one of a few ways to effectively maximise your GSP’s ad reach and performance. Give it a try and share your thoughts and results.
Below are further reading resources by Google Adwords on Domain Targeting:
*Please note: Google has announced that as of 28 September 2017, Gmail ads will no longer be using consumer Gmail content for ad personalization and as a result, you may see a change in your campaign reach, clicks, and conversions. Gmail campaigns using domain targeting are advised to replace domains with keyword targeting to ensure ads continue to show.