Sharing the Gospel: help me Lord!

This week I feel a very strong conviction that I want to share the gospel with my school friends. Perhaps it's the many long days and evenings we've spent together elbow-deep in our revision for the exams. I enjoy their company and friendship so much, and we have grown so close, that I know I cannot carry on without sharing with them the most precious thing in my life, and that would be in theirs.

How do I do this? When is the right time? This is such a challenging, difficult matter. I have been praying that God will show me the right time and the right way to share my Faith with my friends. When the time comes, I just ask that God will speak to me and through me. Isaiah 55:10-11 is great encouragement to me:

For as the rain and the snow come down from heaven
and do not return there but water the earth,
making it bring forth and sprout,
giving seed to the sower and bread to the eater,

so shall my word be that goes out from my mouth;
it shall not return to me empty,
but it shall accomplish that which I purpose,
and shall succeed in the thing for which I sent it.

I hope and pray that God's word will accomplish its work of redemption in the lives of my friends. Quite often, I feel guilty for not being more sincere or serious about the eternal destinies of those around me. Please Lord, show me when and how to tell my dear friends about Jesus. 

P.S: Pastor John Piper gives some guidance on this matter in a recent APJ session.

At what point should I share the gospel with my neighbour?