ETF index funds that are heavily diversified across both sectors and geographic regions are a great place to start - just make sure the total expense ratio stays below something like 0.3%.

Personally, I’ve set mine to automatically invest €500 each month, regardless of what the market is doing. I never try to time it - I just keep buying and never sell. The ones I'm personally buying are iShares EUNL and IS3N with 80/20 distribution.

Index funds.

Start by investing as much as you can afford (even if it’s $5 a paycheck) and find a place that lets you buy fractional shares.

https://www.investopedia.com/buffett-says-index-funds-beat-stock-picking-11724706

https://www.nasdaq.com/articles/warren-buffett-recommends-vanguard-index-fund-it-could-turn-450-month-888200

https://www.cnbc.com/amp/2024/10/09/warren-buffetts-sp-500-bet-paid-off-some-experts-say-it-may-be-time-to-diversify.html