Well I wouldn't say I'm relentlessly efficient but I am improving and one of the things I find the most helpful is just doing small tasks as soon as I become aware of them.
So a party invite is found in school bag: ask DD if she wants to go, RSVP & put in the diary.
A form needs completing and sending off eg for school or council tax or whatever - grab pen, fill in at kitchen table, put in school bag or envelope.
An email requires a brief response - just reply.
This may sound silly to some people but all of the above type things used to go in a pile to be dealt with at some point. Then you have to move the pile, go through the pile etc.
Also with emails make subfolders and move everything that doesn't need action into a folder or delete.
I have found that this means these smaller tasks are dealt with while the kettle is boiling/waiting for the dinner to be ready or whatever and no free/project time is used up. Otherwise when I have time to deal with stuff I start with a list/pile that I have to pick up, read again etc.
The principle is really that you try to handle every bit of paper just once.
I now need to deal with the bigger tasks in a more efficient way too!