Sony DRU510A - what media to use?

I've just bought a Sony DRU510A, plus a few unbranded
-R and -RW to play with.
So far all I've achieved are write errors when using Roxio
Easy CD and DVD Creator 6 to backup some files from
the PC.
Two questions:
1. What factors should I consider when deciding on
-R, -RW versus +R, +RW (my Sony home theatre system
plays all of these (so the book says)?
2. Can anyone recommend media brands that they know
are compatible with the DRU510A - I don't need any more
coasters?
Thanks in advance
David (DVD newbie)