You might benefit from the Email Marketing App.

Learn about it at https://www.odoo.com/page/email-marketing

You could design a journey your new user takes after signing up, encouraging them to discover the value of your product:

Send this after they sign up:

Hi Ray,
Thanks for signing up! With your new account, you'll be able to streamline your daily workflow and start saving time and money.
Check out our tutorial videos [link] to get your first project up and running in minutes and if you have any questions, just reply to this email.
Let's get to work! LOGIN NOW [link]



Send this after two days without signup, or without them logging back in:

Hi Ray,
Creating a project is the first step to simplifying your job. Check out this video [link] to help get your project set up in a few minutes.
The setup is really easy:
1.    Upload your plans in our web version
2.    Create categories
3.    Invite your team
We do a lot of the heavy lifting for you in the background (such as naming plans, linking categories, and optimizing for mobile viewing) so your project can be fully set up in minutes.
Using an iPhone or iPad? Check out our iOS Guide [link].
Using an Android device? Check out our Android Guide [link].
If you have any questions, don’t hesitate to contact us at support@yourcompany.com or reply to this email.
Let's get to work! LOGIN NOW [link]



Send this after five days without signup, or without them logging back in:

Hi Ray,
Just a reminder - creating a project is the best way to get started with us and it’s super easy:
1.    Upload your plans in our web version
2.    Create categories
3.    Invite your team
Watch our video [link] on how to create a project in our web version.
Let's get to work! LOGIN NOW [link]



Send this after ten days without signup, or without them logging back in:

Hi Ray,
Did you know that our active users report that they're saving 6.6 hours a week with us? Make sure you're using your account to the fullest!
To save time and money:
•    Upload project files so you have all the information you need at your fingertips.
•    Use tasks to send notifications to your team of what needs to get done.
•    Invite your team so they'll have the latest plans and rework will be a problem of the past.
For more information on the benefits, check out our blog post [link]. If you want any guidance, don’t hesitate to contact us at support@yourcompany.com or reply to this email.
Let's get to work! LOGIN NOW [link]

You get the idea?

Just remove your free users (or active users if that's your goal) from this journey once they sign up.