Position is more important than number. Until the final few moves of the game, the move that flips the greatest number of your opponent's disks is often not the best move.

One of the key elements of position is mobility: make moves that increase the number of places where you can place a disk, and that decrease the number of places where your opponent can place a disk. The fewer squares where you opponent can move, the higher the likelihood that your opponent will be forced to make an undesirable move.

The best way to increase your mobility, and reduce your opponent's mobility, is to have more "internal" disks and fewer "frontier" disks. Internal disks are disks that are already completely surrounded by disks; frontier disks are disks that adjoin one or more empty squares. Avoid moves that flip a lot of frontier disks to your color, as this will greatly increase your opponent's mobility.

Corners are the most important spots on the board to control. Once you have taken a corner square, your disk can never be outflanked, and therefore never flipped. Always take a corner if you can, and always try to avoid any move that will let your opponent take a corner.

In general, try to avoid placing a disk in the three squares which surround each corner. Even if the move doesn't give the corner to your opponent immediately, it is likely to set up a corner-taking opportunity for your opponent at a future point.

Once you've taken a corner, build outward from that corner, along the sides in both directions, to create a group of unflippable disks.

Taking squares along the side are also important; while they can be flipped, they are more difficult to outflank than pieces in the center of the board, thus limiting your opponent's mobility.

When placing disks along the edge of the board, avoid leaving an odd number of empty squares between two of your disks. This allows your opponent to safely play between your edge-disks, giving your opponent the upper hand in that part of the board.

Toward the end of the game, the board will have several regions of empty squares. It is generally advantageous to place the final disk into a region as it fills up. In order to get in position to place this final disk, it is better to place a disk in a region with an odd number of empty squares over a region with an even number of empty squares.