Vicky,
I'm staying at Travel Inn at Becton at the end of the DLR - normally get the DLR aroun 7.15, up to Poplar, get off and get DLR back to Blackheath along with hundreds of others.
Then , depening on your start , depends which station you get off at - but its crystal clear in terms of signposts, marshalls etc...
Just leave plenty of time, better there early than late eh ?
Enjoy ...