Maybe start by looking at a small problem/time sink you're currently facing and build something around that? For example, I wrote a small script in Python to automatically scrape jobs in the past 24 hours when I was applying for a new role (It return the Company, Job Name, and Job Link).
A web scraper! Wrap your scrape results with an API and boom you'll have cash flow.
* Trello clone
* personal pastebin
* url shortener
* small file storage where you can upload documents and then share url
* HackerNews clone
* Reddit r/place clone
etc. There are tons of them
Fun idea.. take an instagram public profile and classify all the photos for someone using an image classifier.
I say start with a flask app. Then build whatever you think the web is missing.
Start with hello world, then maybe make a website of some kind.