Of all the things that get me motivated to talk about Jesus, one of the most effective is hearing other people's stories of what's happened when they have. If accounts from the book of Acts seem a little distant, hearing about what happened to Bob last week has a more immediate impact.
Real life, personal stories have a lot of power. I've started keeping a private journal of noteworthy happenings at s-yfc, which is a helpful focusing tool.
The conversations with Christians I enjoy most are the ones where we talk about what God has done, and is doing in our lives and the lives of those around us. We often ask our friends "what are you up to?" but isn't it more exciting to ask "what is God up to?" The answers can be really encouraging.
So if you've got stories of witnessing going well, please share them.