据我所知...

Place it at the very start of your sentence. It acts as a bridge to your main point. You don't need fancy grammar here. Just say 据我所知 and follow it with a fact. It works perfectly in both speech and text. It makes you sound well-informed and careful.

Use it when a friend asks for details you might not 100% guarantee. Use it in a meeting to share data without sounding arrogant. It is great for gossip you heard but haven't verified. If someone asks if the cute cafe is open, start with this. It shows you are helpful but honest.

Avoid this for things you definitely should know. Don't use it for your own birthday or address. That would sound very strange and robotic! Also, avoid it if you are totally guessing. If you have zero clue, just say you don't know. Using it for a wild guess makes you look unreliable.

Chinese culture often values 'saving face' and modesty. People rarely like to be proved wrong or sound too aggressive. This phrase is a polite way to offer information softly. It creates a 'buffer zone' between you and the information. It is a sign of a sophisticated speaker who respects the truth.

If you want to sound even more formal, try 据我了解. For a very casual vibe with friends, you might just say 听说 (I heard). But 据我所知 is the 'Goldilocks' of phrases. It is not too stiff and not too lazy. It fits almost every situation perfectly.