Whenever you can, try to centralize inputs, channeling them into a main collector, for example the e-mail. This will allow you to be more systematic in your processing.
"Could you please send me an e-mail with that?" - this applies specially if the request gets you in a moment where collecting it is not really handy (e.g. driving, or at the coffee machine).
Many people also send e-mails to themselves, which can be really smart if that's your main processing channel.
In general, group as much as possible in one spot. Physically also: having an inbox is a must on your desk or at home. Even a special compartment on your briefcase can serve you well as a collector.
As someone who sends myself emails as a way to track tasks, combined this with some very basic auto-filtering is a very good step to controlling inflows.