I'm happy to share my project folder structure with you. This is what I've used in my professional work for years:
The '_main_comp' is made of the parts. As a soft rule, parts are to generally be kept to below 30s in length or a max of 100 layers. I had noticed that performance tends to drop swiftly if you have too many layers in a single comp.
For the assets, 'AI' is for Adobe Illustrator, 'PSD' is for Photoshop Document and 'AE' is for when you need to import other After Effects files into the current one.
If you are still doing a lot of experimenting, you could also add a 'TESTS' folder where you could keep them all organised. Be warned that AE's performance could also drop dramatically if your project file starts to get too bloated with assets and comps. What I would do if that happens, is to save a new version of my project and strip out anything that I think I no longer need. Though you definitely don't want to create a new file for each experiment, as there are going to be times where you want to copy/paste from one to another. Just keeping good organisation, with good naming conventions should be enough.
Using an underscore is a great way of keeping important or more commonly used things at the top of the stack.