It is not that hard really. Just focus on your chest if you want to isolate it. Explore and feel what muscles your body uses to do the isolation. Basic cobra will come to you quite fast!
Nowadays there are even tutorials on how to put on a scarf on youtube lol. So don't tell me you had no luck.
Here are some videos.
Mr. Wiggles tutorial:
Some visual aid:
Kei's basic tutorial:
Kei's advanced tutorial:
Oh, and of course these for inspiration:
Now go and practise!