Planninf my trip to Sweden. What should I take into account?

Hello!

I’m starting to plan my trip to Stockholm in early september and since I’ll probably me travelling by myself and it’s my first time in Sweden, I thought I should come here ask for advice. It’s a trip I’ve been planning to make for a few years and I’m starting to learn some swedish in the meantime.

So: what should I visit? What should I get to know in the city? What areas to avoid? What’s the best place to stay? How to get from the airport (Arlanda) to city centre?

Hit me up with any relevant advices you might have! They’re more than welcome :-)

Tack så mycket! :-)

EDIT: Planning, not planninf, sorry!