I haven't develop any web app using flask but the practices which I follow in order to make my workflow smoother and productive are:

1.) Text editor

A good text editor makes your workflow faster and smoother. I use Sublime-text and make use of emmet along with some packages in order to speed up my workflow.

2.) Work flow

• I firstly design the wire framework of my web app in order to get a clear idea of my web app. I make use of moqups in order to create wire-frames.
• Secondly, I use to design the front-end of my web app.
• Thirdly, I design the database schema and proceed with the back-end development of my web app.
• Lastly I integrate the front-end with back-end and then do the testing.

3.) Modular approach

I use to have a modular approach while developing any web app by dividing different components and functionality into modules so to easily identify the bug when something goes wrong.

General ideas that are relatively easy to make but cover a lot of ground in terms of knowledge :

• Login system - You can learn a lot about sessions, csrf protection, encryption and a lot more while developing a login system.
• Blogging application - You can learn a lot about database and REST API while developing a blogging application.
• Chat application - You can learn about real-time bidirectional event-based communication and lot more.

1. Todo List (spice it up with features like collaboration, sublists and stuff)
2. A CMS (implement REST API as well)
3. A polling web app

You can learn a lot about databases, jinja templating, REST API, session management with these projects.

In addition to the other great ideas, you could try

• multitennant time-tracker
• RBAC to allow different kinds of administrators
• break up the system into a separate frontend and a backend systems. (microservices or api gateway structure)
• Try to use only static files for the front-end

A pokedex app for real animals (users can cross off the ones they have already seen with their own eyes).