I've long been an advocate of writing down everything. Write it in your iPhone, on your Mac, on an index card, in a Field Notes book — whatever. Just write it down. Capture, if you prefer.
"It" being anything that seems like it might be useful later. An idea, a thought, something you want to do.
This concept extends to reading as well. See an interesting article? Send it to Instapaper. You can read it later.
Eventually, with all the writing, capturing, and Instapapering, you have a giant pile of stuff to deal with. More specifically, you have a giant pile of stuff that a past version of you decided was important.
That's a really important distinction.
You didn't save this stuff for later. Someone who looks like you did. Someone who thinks mostly like you did. Someone who has similar, but slightly different priorities than you did.
This stuff was important to that person. It's probably important to you, but it's not definitely important to you.
Before you put your head down and start knocking out those tasks or reading those articles, take a moment. Take a moment to make sure the thing you're about to do is still important. Make sure that the current you still wants to do it.
If you find out that you don't want to do it, delete the task. Delete the email. Delete the 90 page article in Instapaper. Delete it and move on to the thing that matters to the current you.
Future you will thank you for it.