The Hills
6 Jiten Pazar Street
For starters enjoying the sunset from all the different hills is a must. walk all the way to the top in the late afternoon, pick something to drink and stay there for the sunset. go down to enjoy the nightlife once it's dark.
Plovdiv offers many things to do, and most are easily walkable.
Old Town
Another must is the old town of plovdiv which is full of art, free of cars and very enjoyable. go take a walk try it at day, try it at night it's amazing. try some of the bars there are life performances sometimes there. you might be even lucky enough to catch an opera performance in the old roman theater.
Center
Enjoying the central park during the day, especially if it's a very, very hot day. once the weather settles hit the main street and the bars/discos.