Definitely ask, my current gf was shocked that i took so much interest and asked so many questions about what pleases her. Turns out, i found out quite a few things i would never have guessed, like lightly stroking her stomach/pelvic area is a real turnon...I had no clue...I lightly stroke areas of skin, but it would never occur to me that her stomach was so sensitive
unless it's a one night stand, just ask. if it's a one night stand, she'll tell you