The 10 golden rules for Blokus
At the beginning of the game, try to move towards the center of the board in order to occupy a maximum amount of space. If you remain confined in your starting area, you will be blocked very quickly.
Try to place your large pieces on the board at the beginning of the game. Towards the end of the game, space is rapidly shrinking and you may not be able to find room for them.
Don't forget that one of the most important elements is the position occupied by the corners of your pieces on the board, which enable you to make your next move. Think about keeping a maximum of “free” corners to always have possibilities to extend your territory.
You will rapidly see within your opponent’s lines some strategic points that can give you a path to another part of the board. Be the first to capture them and enter new territories.
When playing with two sets of pieces, try to block one of your opponent’s colors by using your two colors together. If you succeed in this strategy rapidly, you’ll certainly have enough space then for your own pieces by the end of the game.
Block your opponent by covering his or her most advanced corners to prevent him or her from moving forward. Note: Know how to be patient - it is sometimes better to hang back slightly from the opponent's pieces and let your opponent become exposed so that you can then block him or her more effectively.
Take note of the squares where no other player can play and keep these spaces in reserve (with the corresponding pieces) and play in another area. You can always come back to them later.
Play according to your remaining pieces but also according to your opponent's remaining pieces. It could be that an empty area cannot be exploited by your opponent if he or she doesn't have the necessary piece.
The small square alone is a key to enter any new area when you are blocked somewhere. But remember that this key is unique: you can play it one time and one time only. And remember that you do not use it as a key, that is to say if you keep it fro your last move, you’ll gain bonuses that probably will make you the winner.
Remember that finishing a color earns you fifteen points and will even earn you twenty points if you finish with the single square. Check whether your opponent can achieve this, and if so, try to stop him/her even if this means you will be unable to place some of your own pieces on the board.
Reference: the Tips Section at www.blokus.com