Early Game Strategy
When playing Internet Reversi, do not be too concerned about having more pieces than your opponent early in the game. The player with the most pieces at the end of the game is the one that wins. If you have a lot of pieces early in the game, it will give your opponent a lot of options for where to move on the game board to capture your pieces. Gamblinggates.com indicates this strategy makes it easy for your opponent to choose plays that do not give you the chance to win valuable side and corner locations. The fewer pieces you have on the game board, the more likely your opponent will be forced to make a play which will give you a chance to claim a corner or side.
The Danger Zones
Avoid playing one of your pieces into the three adjoining squares of a corner whenever possible if the corner does not already have a piece in it. Tthis can make it much easier for your opponent to claim a corner. Even if your opponent does not have an immediate play that would allow him to claim the corner, those pieces adjacent to the corner will remain your color until someone plays into the corner. The more pieces you have adjacent to the corner, the less likely you are to be able to claim the corner.
Control The Center
Keeping control of the center of the board will maximize your number of potential moves later in the game. By keeping your pieces in the center of the table, you will make it harder for your opponent to get the edge and corner pieces. Try to avoid playing your pieces on the rows adjacent to the edge spaces early in the game. Also be aware of any moves that you make flipping your opponent's pieces in these locations early in the game. If you claim an edge piece early, try to protect it by claiming another piece close by, but not adjacent to it.