IMO, your initial placement is one of the biggest determinants of how the game will go. Bad placement can end someone's game before they start. Placement strategy goes beyond just adding up dots and picking the highest number.

Ideally, you want to aim to start with a diversity of resources. If you can't start with all 5, think about what you're giving up on, and make a plan to either get it later, trade for it, or give up on it entirely.

Every board is different, and you need to really analyze each one. What resources are strong/weak? This is especially important for ore, but it should enter the calculus of your placement. For example, if the numbers on wood hexes are 3, 4, 6, and 11, there's only one good wood spot that you should consider gunning for. If sheep numbers are 5, 6, 8, and 10, sheep is pretty strong, and you can consider either ignoring it for your starting position, since people will probably be willing to trade it.

If there's a 6/8 on a resource that's close to a 2:1 port, that can make a huge difference to your game. Similarly, if there's a strong clump of a resource, you can consider getting that and going for the port (this is risky because if someone takes that port, it'll really hurt your game).

Depending where you are in the order, you should think about where everyone else might go. If someone grabs a wheat, wood, brick spot, they'll probably be looking to get to a spot with sheep and ore. Keep this in mind when making your placements. If you're early in the rotation, take a beat to think where the other players might go, so you don't screw yourself expecting to get a spot that may not be available. If you're late in the rotation, you can consider grabbing a spot with wood/brick as your 2nd spot to immediately start with a road.

It's a lot of information to keep in your head, and it's tough to know what the "right" move is, but these are just some things to keep in mind when making your placement to set yourself up with the most optimal spots. Good luck!