Don't hang your pieces

A 'hung' piece is one that can be captured for free — nothing defends it, nothing threatens back. Hanging pieces is the single biggest reason beginners lose games. Beating the habit costs nothing: just look before you move.

After every move you're considering, ask the same question: 'If I play this, can my opponent just take something next?' That's the whole defensive habit. World-class players basically do this at superhuman speed.

It also works the other way. After every move your opponent makes, scan their pieces — is anything sitting on a square where it's attacked more than it's defended? If yes, that's your move. The free piece you grab is often the move that decides the game.