We’re at the half way mark of this thing now. And the openings are finally being played! Which means I’m going to talk about playing Connect 4, which you probably don’t care about.
If you presume your opponent hasn’t memorized the perfect play – which is probably a safe bet – there’s a couple of different openings in Connect 4. The best one, though, is to build a zigzag upwards in the centre two columns: this gives you maximum coverage of the board throughout the rest of the game, like controlling the centre in Chess. It also means that to stop you getting an easy connection early on in the game, they have to keep blocking you, thus aiding in your zigzag.
Of course, this means that your opponent also is building a zigzag: but if you initiated it, you’ve got the drop on them by one move, and a good use of that is to start building out to the side to connect the lower parts of your zigzag together. You have to pull away from the centre and do that before your opponent does, though; otherwise you’re playing catch-up to them. So it becomes a question of deciding on the opportune moment to balance the two, which depends on what you know of your opponent.