As the others have said, under normal operations, you will arrive on the eastbound Jubilee line platform 6 and just go up one level to the DLR platforms, where platform 3 has trains alternating between going to Woolwich Arsenal (which you want) and Beckton (which you don't want).
But beware that Canning Town has two separate pairs of DLR platforms. This picture is taken from DLR platforms 1 and 2, and shows how it sits separate from the stack of DLR platforms 3 and 4 on top of Jubilee Line platforms 5 and 6:
Obviously you want to avoid going to platforms 1 and 2, as to get there you'd have to go down from the Jubilee platforms to the subway, then across, and then up again to the DLR platforms. Depending on the time of day, trains may also run to Woolwich Arsenal and/or Beckton from platform 1, so you should just ignore them unless there's no train from platform 3 due to disruption.
If you're coming back the same way, then before you board the DLR train towards Canning Town, have a look at what its final destination is. Bank or Tower Gateway means it will go to platform 4 and the Jubilee line is just one level below. Stratford International means it will go to platform 1 and 2, so you might want to take the next train instead (provided there is one for Bank/Tower Gateway showing on the departure board).