Abstract strategy games are some of my favorite. I cannot think of a simpler game from that genre that packs as much strategy as Blokus does.
Place your Large Pieces First
Once players start taking turns and branching out from their corners, space will be at a premium. It makes sense to use your large pieces first. Blokus comes with twelve pieces that are five blocks large and these should be your priority in the first few turns. Some pieces will be easier to place than others due to their shape but you do not want to be hanging onto one of these when the game is nearing its end.
Get to the Center of the Board
This is paramount. Failing this means that you are already severely limited in your ability to win the game. If you stay in the area that you begin the game, you will be blocked easily. Like Manifest Destiny, you need to stake out and claim all land; even if it’s not “yours”.
Have More Than One Option
When placing a piece, you know a future piece will be played off the corners of that one. When possible, try to leave yourself at least two (preferably more) placements off of that piece. You do not want to be pigeonholed into only being able to place one particular piece then have an opponent occupy the area.
If an opponent leaves a space open, take it. Blokus can be confrontational but it’s just a game.
Sometimes it might be worthwhile to let your opponent overextend themselves into your area so you can block them. You fool your opponent(s) into thinking you’re fine with letting them encroach but in reality, you’re waiting to strike.
See where your opponent(s) cannot play or reach. Set aside (discreetly) pieces that can be played there in the future so you don’t end up using them elsewhere.
Don’t Waste the Single Square
The single square could make or break the game for a player. Even though it provides a bonus by being placed last, it could also be the difference between first and last place if used to spring a player to new real estate to lay other pieces.