My first-ever scifi book was Return to Mars, by Capn W.E. Johns (of Biggles fame). I got it on my first-ever visit to the local library, which I had just joined, aged 6 or 7. This book just blew me away! It tells the story of a boy who goes to Mars with a boffin - can't recall why now. Here they meet an alien, a 'good guy' named something like Vargo. I then spent the next year or so getting hold of the rest of the series via book request! Later I bought Return to Mars, which is still on my shelves.