A Chinese friend of mine now helps me with my Chinese and I teach her my native language in return. However, at the moment, we both don't have too much of a structure and I feel that it's currently still rather inefficient. I use the NPCR 2 and I guess I'm currently more or less on HSK 3 level. Anyone got experience with Tandem language learning and some ideas on how to improve the quality? At the moment I read texts with her from the book, do some oral exercises but what I'm still lacking are regular conversations because I'm currently not yet able to come up with all the words I wish to say.

The quality and structure especially of tandem learning is highly depending on your own and your partners input.

one idea would be that you do some reading exercise first, let her explain the new words, then later practice them on your own.

as second part of the tandem learning I would suggst to put the book aside and just "chat" with the language partner like in an everydaylife situation.

I guess you both use English. In this case you could just try to express yourself in Chinese and when you come to a word you dont know yet you could ask.
Tell her the word in English and she will come up with the Chinese equivalent.

Good luck!

The FSI Mandarin course has lots of role playing and other exercises that lend themselves to working through them with a partner.

This is the link, though it doesn't seem to be working today: http://fsi-language-courses.org