Taken from Attacking & Defending Moyos by Rob van Zeijst & Richard Bozulich

“The big moves are: 1. Occupying the empty Corners; 2. Approach moves; 3. Corner enclosures; 4. Extensions along the sides; 5. Moves played into the center (these are the ones that build moyos).

Urgent moves are those that defended weak groups, giving them the resiliency to withstand an attack. By extension, finding a weak group of your opponents and attacking it must also be an urgent move.