1. Log into SteamDB
2. Open this link, which shows the games you own with fewer than 500 reviews (or change the number however you see fit)
3. Pick some small/indie games you liked from this list
4. Go to Steam and review them

Every review helps!

https://steamdb.info/sales/?displayOnly=OwnedGames&max_reviews=500&min_discount=0&min_rating=0&min_reviews=0&sort=release_desc