For people who already read music (not necessarily fluently, but reliably) learning to sing from written notes is an interesting skill to develop. (If you are not sure about basic piano skills, a few weeks of such study would be a good place to start).

I find the traditional solfege (moveable "do") to be an accessible and useful way to develop sight singing skills.

Solfege is the system of learning to recognize and to hear melodies in terms of the syllables "do, re, mi, fa, sol, la, ti, do" (think major scale) that used to be taught in our schools, and still is in many European educational systems. 

Each "syllable" (do, re, etc.) has its own aural characteristics, and learning to recognize these not only leads toward sight singing skills, but also toward richer ways of hearing any music.

 Talk to Betsy about a sample lesson.