Not all tops are made for traditional bras. Sure, you could always wear a strapless bra. You can buy specialty clips that hide your straps, too. But if you don't have either, a simpler option is to just use a paper clip.
I heard about this tip from a friend, but this YouTube video shows how it's done. Hook one bra strap through the end of a paper clip under your shirt. Grab the other strap and hook it to the other end of the clip.
Easy fix, and your straps stay bundled and concealed under your top. Check out the video to see for yourself.
bra straps and paper clip [Susan Hernandez (YouTube)]