This is an impossible question to answer as there is no one size fits all answer. This can depend on your investment goals and personality. You will need a completely different strategy for money you might need in a few years than retirement money in 20 or more years.
Your personality will also have a huge impact. Do you want to research your own investment ideas or have someone else pick your investments? Do you want to be aggressive and high risk, or conservative and stable?
Figuring out your investing personality is very important, and this can be a process of trial and error. The most important thing for an investment strategy is to try and stick with it, though within reason of learning from your mistakes. You will not want to go chasing the latest investment scheme.
The best example of this is mutual fund investors who are 'jumping ship' too often. Even the best fund managers will have bad years. But their excellent years will offset those bad ones. Peter Lynch was the superstar fund manager of the 1980s. I have read that most people invested in his mutual fund underperformed, even though he had the #1 performance for the decade. These investors would buy when his fund was hot and sell when it struggled... they were buying high and selling low.
One of the most famous investors said something to the effect: "you make the most money through sitting". In other words, you do your homework and then let your investment reward you.