>>27
It's important to ask questions so that he is more likely to reply...ask him what his interests are(books, music and other such things) Ask him what he thinks about in prison and stuff like that.
I also think you should include your age(There isn't an age limitation is there?)so that he has an indication that he is loved by a whole new generation ^^
I'm not saying you should put all that in one letter.
Oh yeh read this somewhere as well- In many prisons these days they are allowed to receive stamps, envelopes and even writing paper to help cut down on the costs of replying to letters.