The scramble at Canada Water for the solo escalator to the Jubilee line can be avoided by going on the escalator up to the ticket hall, which you'll see from the front carriage of the train as it arrives. Take that up, then you'll see the escalators back down again. This trick during the peak can be faster than waiting on the Overground platform to get down there.

As for me personally, I travel on Southern to London Bridge and it's never been so good since the introduction of the Overground. 9 times out of 10 I get a seat in the peaks.

Another trick if you're using the Overground route in the peaks is to board the Highbury and Islington trains. These start from Crystal Palace, so don't have as many passengers on them. As suggested above, wait at the front of the platform at FH/HOP. On the way home, board the Crystal Palace trains near the end of the platform. Again, these are less busy (although you may still have to stand) but are more bearable than the West Croydon services.