The Power of the Center
In Connect 4, the center column is the most powerful position on the board. Why? Because an odd number of possible winning lines run through the center column. Taking the bottom-center spot on turn one is the mathematically strongest opening move.
Creating a 7-Trap
A "7-Trap" involves setting up three of your discs in a shape resembling a "7", where placing a disc in the exact corner completes two possible 4-in-a-row connections simultaneously. Because your opponent can only block one, you are guaranteed a win on your next turn.
Control the Odd/Even Rows
Connect 4 is a "solved" game, meaning that with perfect play, the first player can always force a win. A major part of this involves Zugzwang—forcing your opponent to make a move that benefits you. Controlling the even rows if you go second, or the odd rows if you go first, is key to manipulating the late game board state.