The part that goes between your butt-cheeks should actually go between, but certainly not cutting into you. Also, the sides should fit well around, but not tight enough that they press into your flesh and create bulges above that look like low love-handles. I wear thongs daily...I notice that when I have gained a few pounds or am retaining fluid (PMS or too much salty food the day before), some pairs are too snug. Keep that in mind, too, because you may have a few pairs that will be good for some days and bad for others. Once you have been wearing thongs long enough, you will know what feels right. Well-fitting thongs should be extremely comfortable. And, once you are really used to them, and you switch back to regular underwear for whatever reason (I like to wear the old-fashioned stuff when I am hanging out at home in my sweats), the former stuff will feel somewhat bulky (although cozy). Say bye-bye to panty-lines!