What to Talk About
If you're still stuck, get ideas from people. Sometimes hearing another person's story will spark ideas of how to tell your own. Tell 3 will be featuring stories of other people's experience Telling 3. In the meantime, the Human Rights Campaign's web site features the stories of LGBT people talking about relationships, coming out, school, work, parenting, aging and other topics. 10 Couples features same-sex couples telling their stories, as does Freedom to Marry.
One conversation to avoid is a political debate. By all means, talk about LGBT politics if it's part of your personal story. But don't get into a purely political argument with someone (or do, but don't count it as one of your three). Conversations about rights and equality have their place, but they're abstract concepts and don't change people's hearts and minds the way personal stories do. Said another way, a story about not being allowed to pick up a prescription for your sick partner or how the head of your division stopped inviting you to his annual Super Bowl party since you came out are better than talking in general terms about workplace discrimination and marriage rights.
Resources for Straight Allies
GLAAD: Be an Ally & a Friend - www.glaad.org/ally/index.php
PFLAG: Parents, Families and Friends of Lesbians and Gays - www.pflag.org
GLSEN: Ally Week - www.allyweek.org