From now on we will be talking about the 19x19 board. If you are still having fun on 9x9 there is no rush to switch. You can come back whenever you want.
Play in this order: Corners, Sides, Center
This does not mean that if you start near a corner and your opponent doesn’t that you win automatically but it should start you in the right direction. Generally speaking, we first look to take the corners, then the sides and lastly, the center. In Go there is an exception for everything but it is very good to keep this general direction in mind. We call moves that have the potential to surround a relatively large area on the board “big”.
One possible exception to this approach is when there is a stone (be it yours or your opponent’s) that’s in trouble. If the stone is yours, you must save or help it. If the stone is your opponent’s, you should attack it. We say play urgent moves before big.