I've been on an HSA+HDHP for a couple of years now and only realized recently the interest earned from investing HSA money is also tax free, so I want to start investing a part of my savings and see how it goes. I have 2 options, Betterment or Mutual Funds. I figured I'd try the latter to avoid fees, but I'm not sure which funds to choose. My HSA currently provides 30 fund options.

I see people mentioning Vanguard a lot so I spread out my initial investment into 25% chunks across 4 different Vanguard funds. How did I choose them? Well I literally just looked at the performance graphs and selected the ones that historically went up steadily without major dips. As a total noob, how can I improve my choices? Is there a simple way to decide without having to dive deep into the stock market?