Something that has worked well for me: creating a Charles Schwab account and setting it up to automatically transfer x dollars from my regular checking to their account. Once that was setup, I configured it to automatically buy 0.9x dollars worth of their Schwab index funds every month. It has performed well through thick and thin since I set this all up a few years ago.

The remaining 0.1x I leave in there as a buffer/short term savings. I don’t have a convenient way to access that money (debit card, checking, etc.), so it’s a good rainy day fund that I can transfer to my regular bank account if I need it.