To gain the most value from Google Tag Manager, you should migrate all (or as many as possible) of your existing tags into Tag Manager. The recommended steps are as follows:
Map your site (optional)
Think about which tags you might currently have deployed on your site. Think about what actions (events) you want to track and what data (variables) you'll want to collect. Create a map of tags, the data to be collected, and which events or pages you want to associate with those tags.
Install the Tag Manager code on your site
Once you've mapped your site, install the Tag Manager container tag on your site and deploy it. Read the installation guidance for more information.
Add Events and Variables
Customize your Google Tag Manager installation using the methods outlined in the events guidance.
Configure tags and their associated triggers in Tag Manager
Once Tag Manager is installed on your site, you should add your site tags to the user interface. DO NOT publish at this time. Simply add and configure the tags from your site in Tag Manager with appropriate tag templates and triggers. Learn more about triggers.
Final migration swap
The last step is where you simultaneously swap out your old tags and publish your tags in Google Tag Manager. Within a few minutes of each other, you'll want to:
- Remove your site tags in a single code push
- Once you know this push is successful, press the "Publish" button for your container version.
This method might cause a small gap in data, but once the initial swap is complete, no more gaps will appear. Alternatively, you could swap the order here and publish shortly before your site changes go live. This might cause minor, one-time data duplication instead of a small data gap.
After you've completed the initial migration to Tag Manager, any subsequent tag configuration needs can be handled without code changes via the Tag Manager interface.