This is my (simplified) project list (only “Templates” is a tag)
The “Templates” contains the templates for creating a contact, an opportunity and a deal. You can have multiple type of opportunities and multiple type of deals here
The template for the contact has few fields and a step-by-step guide that trains every user (even the new one in the company) on how to create a contact. Please note that this screenshot has the details in the description and not in some fields as it is in a free account.
The template already contains a list of subtasks that are generally used (in my case I always try to keep in mind the important dates)
The template for the opportunity is similar. It explains step by step what to do after duplicating the template and make it a subtask of the contact it refers to
Each opportunity has a list of subtasks we use to make sure to provide the best experience to the contact (without forgetting so send any info) and to higher the chances of transforming a lead in a customer
The Deals are structured in the same way (apologies, the template of the deal contains sensitive info that can’t be published, but you can define the subtasks of each deal to mirror your business and everything you need to do to navigate your clients to a positive sale process)
In the Contacts project I keep all the contacts. As mentioned above, as this is the free version of asana, used for creating these screenshots, I don’t have the custom fields. In “Contacts”, “Opportunities” and “Deals” I don’t have subgroups, but I use a custom field in the contacts, opportunities and deals tasks to define their status!
When I create a new contact, I can use the Opportunity and Deal templates as subtasks of the contact. In this way I have a complete vision of a contact, every note and opportunity neatly folded in the same view 
Duplicating a template (an opportunity in this case) gives me access to all the subtasks I need to work on. No fear of missing something I have to do.
Each opportunity is stored in the “Opportunities” project as well. In this way I have an immediate view of all the open opportunities and their stages
Same thing goes for the Deals. If I want to see which deals I am working on, I just check the Deals project, and there they are, neatly organised (in here I organise them manually, in a pro-account they are automatically organised with a custom field).
While I don’t think this is the simplest way of doing things, this I have shown here is the best way we reached so far to higher our chances to win customers and provide them the best end-to-end experience. It supports multiple opportunities and deals per contact, and it can be expanded to support companies as well.
Every subtask in each Opportunity, Deal and Contact has a similar step-by-step guide that makes training of new employee in our company (this I use for my photography business) a breeze!!!
Hopefully you will find this interesting, and any suggestions you may have to make this structure better is welcome! I am always looking for ways of making my processes better and leaner!
Ciao,
Carlo