Never underestimate the erotic power of the neck and back. But also be careful with them.

The sides of the neck near the jugular veins/carotid arteries and the center of the back traveling down the spine are two major erogenous zones of the body. Don't be afraid to kiss, lick, or gently caress those areas during foreplay. This applies to both biological sexes.

Of course, as with everything, get enthusiastic consent first. Some people are too physically sensitive in those areas, and those are some of the most common areas where people are touch-averse due to some kinds of trauma, so ask during the act if you can touch them.

If you're kissing lip-to-lip, putting your palm gently on the side of the neck as you make out is a great way to enhance the experience for you and your partner.