What is the best investment tip you ever got?

Time in the market is always better than timing the market.

Don't ask a barber whether or not you need to cut hair. HAHAHA

Basically do not listen or believe people who does not have your interest at heart or have conflict of interest.

None really. More like investment wisdom, since tips sound almost akin to insider knowledge!

There is some truth in the common adages, which have been mentioned in the other answers.

Amongst the ones that apply to me most would be

• Be greedy when others are fearful, be fearful when others are greedy

• Investments should be boring, then you know you will be making

• Buy at prices you would not sell at, sell at prices you would not buy at.

-to buy with ultra longterm buy&hold strategy largest&cheapest well diversified passive indexing stock ETFs