Working in the IT field I come across an unimaginable amount of data on a regular basis in just dealing with day-to-day issues. Any task is like that these days - and especially to someone who knows nothing of the task until it's presented.
The main thing to remember here is organization. The method you use to organize the data is not important - only that you stick to it for the most part. If something doesn't fit then you either change the item you're having a problem with...or you change your system of organization.
Ever watch a flock of birds? One thing you'll notice is that if you try to focus on all the birds at once you'll most likely get confused. If you focus on, say, one bird out of the flock, then you've mentally organized that one bird out of the flock. Guess what...if you keep adding birds out of the flock until you've looked at them all then you've organized the flock in your mind. Information in the day-to-day world is no different.
Breaking down information into chunks you can deal with is absolutely vital to understanding and remembering. After all, without training you couldn't recall a whole book from memory, right? But you could recall important parts of it. Eventually, if you keep adding to those parts then you would at some point recall the entire book. In another context, this techique has been known for roughly two millenia. Remember the Latin phrase divide et impera (divide and rule)?
Now, how this relates to sifting is most of the time pretty simple. Organize the data, but focus on the stuff you want. For instance if you want to observe only the red birds in the flock then focus on the color red. Sounds pretty easy right? Well...yes and no.
When dealing with large amounts of data you have to do a little estimation of chance up front.
What's that mean? Let's say your family bakes a pie with a ring in it for the holiday. Whoever gets the ring wins a prize. You really want that prize so you focus on the ring. Thus you ask some questions of yourself:
Does the ring have any special properties I can use to identify it?
Does the ring affect the piece of pie it's in in any way?
Is there anywhere in the pie I know the ring is not located?
Suppose the ring is copper and turns the pie green. Then you know that any piece of pie that is the normal color is less likely to have the ring in it.
That narrows your focus by a certain amount.
Suppose the ring is also pretty big, so the pie bulges where the ring is. Then you know that any flat piece of pie will not have the ring in it.
That narrows your focus again.
You keep going with this method until you've found the ring.
Some things that help this process:
Learning to speed-read. There are plenty of courses out there for this.
Good language skills for the materials you're searching.
Frequent breaks. Spending too much time sifting often blurs your focus.
Focus on one thing at a time. You get more done that way. Remember, sunlight spread out only warms things up, but sunlight focused on one place with a magnifying glass can burn holes in things.
Know what you want. Know what you are looking for. If you don't know, how will you know if you find it?
Delegate. Get people to help you. Parallel searching is helpful, as long as you make sure they know what they are looking for.
It's horribly cliche, but big mountains are just piles of pebbles stacked on top of each other. Information is the same...