Have you ever walked in on your partner masturbating? Was it a turn-on for you? If so, why not try it in the bedroom?
Even if you don’t make it all the way to orgasm, watching someone else get off is a good way to learn what ways your partner likes to be touched, and you can kiss and fondle your partner with your other hand at the same time.
Also, looking into each other’s eyes or at the genitals while you’re touching yourself is a good way to build sexual tension.