How do I get more rain in my barrel?

[Bigmallly]

If you go for the down pipe option make sure you can get rid of the overflow from the butt. I have a 500ltr butt which feeds two 100ltr butts, fed from a down pipe from about a 15m long roof and in the winter I have to leave the tap draining into a hose so I can get rid of the excess water

If a divertor is fitting to the downpipe correctly, there should be no need for an overflow as it has one in-built into the system. It is designed in a way that once the butt is full, any excess water will continue its journey down the drain.

[ESBkevin]

The distance it has to fall and the angle that it will pour off the end with a decent flow means there will be a lot of loss/spillage. Often when it rains hard there is wind too!
A simple plastic chain (with a bolt on the end to weigh it down) or lightweight metal chain or similar from inside the gutter down into the water butt will 'guide' the fall of water better. Putting a proper downpipe would be better still and having similar the other side of the pitched roof would be best.

[degsy]

Block the other end of your gutter that should help good luck!