What NOT to do in Vienna

Hi Everyone!
I’ll be spending a weekend in Vienna on the next July and as it will be my first time in this beautiful city I am trying to gather some infos about tourist traps and things not to do ;-P
So far I have read some interesting tips: from the airport it is better to get the S-Bahn rather than the CAT, the 72hrs ticket (Wiener Linien) is much cheaper than the Vienna Card (provided you don’t spend all 3 days visiting museums, which is not exactly my plan….).
Is it then true that the Sacher Torte by Griensteidl Cafe or by Oberlaa Kurkonditorei is much better than the one of the famous Sacher Café ??

Any help or suggestion would be greatly appreciated! :-)

Kind Regards,
Linda