OK, here would be my approach:
1) Make a list of every country represented in the collection. If you come across something from somewhere you can't identify (in a non-Latin alphabet), there's a free iOS app called Stamp Identifier that can probably help (you take a picture of the stamp and it matches based on appearance).
2) Do your best to organize by country. Having to hop back and forth between countries, flipping 200 pages at a time, is a PITA. There's a lot to be said for saying you've checked all the "A" countries.
3) Borrow one or more Scott catalogs from the library, or buy cheap at a used book store, or open a free account at stampworld.com . If you buy/borrow, it doesn't matter if the edition is a year old or twenty, you'll looking for "exceptions," those stamps or their variants that are listed for $50, $500, $5000, or more.
4) Figure out what your threshold is: since each PSE cert costs $20-$32 at a minimum
, consider something pretty high, like $250 or more. No one care about a certified stamp that has a Scott value of $10, you waste your money getting that certified. Certification doesn't of itself make a stamp more valuable; it only removes (most of) the buyer's doubt about the genuineness of the stamp in question.
5) Now for the real work (fun?). Do your best to match each stamp in the collection with what's in the catalog or website. Doesn't have to be exact, countries often issues that seem identical but for perforations or color or watermark or paper type (for example, the "normal XYZ issue is worth $0.25 in orange but in orange-yellow is $5000"). Anything like that, or anything that might have real value regardless gets put aside for further consideration.
6) You'll quickly have a pile of stamps you can sell, if that's your intention. There's a few bucks to be made by selling consecutive runs by country, like "Ethiopia Sc #135-155, used" on eBay
, for example. Honestly, odds are that 99.5% of the stamps will be in this pile.
7) What's left will be the "hopefuls." These will take a little time and patience, and perhaps some tools like a perforation gauge, watermark detector, and this forum, to suss out.
The most important thing to remember: the stamps aren't going anywhere. Don't stress about this. Spend 30-60 minutes a day if you can, it'll all get done.