Please help a beginner learn strategy for 1v1s

Hi everyone, I'm a beginner catan player. I play exclusively 1v1s against a friend but they always beat me. (Currently playing 1v1s on colonist.io to practice) I know the basics of the game like all the cards and ways to get points. I've tried the ore/wheat strategy and the 2:1 port strategy but I don't know which strategies to use when and how to use them effectively. I always seem to fall behind in one aspect and then get stuck in a chokehold for the whole game. Like I get fenced in on a corner, or I don't have resources to build anything, or they have so many development cards that I'm always being robbed.

How do you analyze the board and know which strategies to use? Should I be going for all of the resources or rely on trading with the bank? How can I prevent falling behind and getting shredded?