As the names imply, the underboob is the lower part of the breast, and the side boob is the outer edge the side near her armpit. Get your lips, tongue, and teeth involved as well as your hands. You can also try blindfolding her, and touching her breasts with different toys or materials. Nipples are sort of like clitorises: some women can hardly stand direct contact, while other women need very firm pressure. The same goes with kneading. This area tends to respond best to delicate touch. You can use vibrators or feather ticklers to create new sensations on her breasts.
Arianna. Age: 24.
The same goes with kneading.
Allison. Age: 28.
Again, start off gentle, and gradually increase the pressure until you find what she likes. Spend some time tracing her collarbone with your finger, then kissing along it. Get your lips, tongue, and teeth involved as well as your hands. She may not want any breast contact for a while, or she may need you to be much more gentle than usual.