Best ETF’s to pair with VOO

I’m 20 years old and currently 100% into VOO, started investing about a month ago. Planning to put about $1,000 into ETF’s / month. I want to withdrawal this money in 10-20 years or something and have good money. What other ETF’s can I buy alongside VOO? I constantly hear you should buy more than just VOO for more exposure. Thank you. General advice is also appreciated.