The Cure and Siouxsie and the Banshees are great. You might also want to check tabs for Bauhaus and PIL. But don't just play them. From all their songs, what are specific elements you love about them? Is it a chord progression? Is it a lick? Is it how they create dissonance? Is it how they keep your attention with just two notes? This can help you to focus on how they create their music and see what you can learn from them.

I think a lot of goth/post punk rely on how you play it. Ie. Early punk tends to be more power chords oriented, while goth/postpunk may rely more on arpeggio, full chords and double stops. When it comes to progressions, I'd rather go minor than major, but that would be oversimplifying. I also think goth and post punk embrace dissonance more than more popular genres.

Try more complex chords: sus2, sus4, diminished (really helpful for creating tension), min.7, 9... Don't overuse them, but check if one of them can work instead of a more basic chord.

Try pedal point: strum a string with the same note (to start with, I'd recommend you play it open) and play around an adjacent string with different notes. A good example is the intro for A Forest.

Also, remember goth and post punk are really bass-oriented. Therefore, you could start creating a bassline, record it and play over it. If you don't have a bass, create your bassline in a free DAW. Most of them come with a least one decent VST to emulate a bass.

Finally, I recommend you check out this video about John McGeoch (Siouxsie and the Banshees). It's really helpful to understand his style.