I thought I would share some travel tips/information (public transport) since thats the first thing I try to find out when I'm at a new place.
If you're in Stuttgart for 2-3 days, getting a Stuttcard is a wise option. With a Stuttcard you can make unlimited trips inside the city using public transport. You would also get free entry at some of the museums around.
At a subway counter, you may purchase a day pass. You can make unlimited trips for a day using any mode of public transport.
I bought a 2-zone day pass since I would not do a lot of traveling. You could find out the zone map online by searching for 'Stuttgart Zone Map' on google
For more information on Stuttgart you could refer - http://www.stgt.com/stuttgart/trans_city_transport_eng.htm
Helpful mobile apps
You could download the VVS application from your mobile app store. It will help you to plan your travel and check the transport schedule.
Food and Drinks
I was fortunate enough to enjoy the spring fest (Frühlingsfest in German). Its a week or two of fun, food, rides and bier (beer). Apart from eating and drinking at different places in the fest, I really had fun in one of the tents (it is an enclosure, somewhat like a circus tent, where you could listen to live music while sipping on your favourite drinks).
Have you ever feel like standing on a table and dancing after having few drinks? If yes, you can do it here, and you won't be alone. In fact, you'll be the odd person out, if you don't :-)
If you happen to visit during the festival, do try to get hold of the traditional costume that locals wear, you'll be taken care of pretty well :-)
As it starts to get warmer, most of the restaurants open up Bier-Gartens in the open space outside. You could enjoy some food and beer while taking a break from the heat.
Places to visit
Since I didn't have much time, these are some of the places I visited, you may find many more things to do.
Walking around Schlossplatz
Mercedes Benz Tower
Mercedes Benz Museum
Frühlingsfest (during spring)