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).
* Trello clone
* personal pastebin
* url shortener
* small file storage where you can upload documents and then share url
* HackerNews clone
* Reddit r/place clone<p>etc. There are tons of them