Some countries definitely are more collectible these days than others and worth separating out into country lots. China is the most obvious example I can think of. Lots involving colonies (French, British, Italian, Spanish) also might be worth separating.
I'd say it's hard to give more specific advice without knowing more about the amount of stamps you're talking about, their desirability, and how they're organized.
Loose stamps in a cigar box, I'd probably just sell as a cigar box full of stamps. Good assortments for beginners, and even though more advanced collectors know they're unlikely to find jewels, or even many better items, they often will enjoy hunting for varieties and cancels. If you have glassine full of foreign stamps, and a quick inspection of a few of the envelopes doesn't turn up much that catalgues for over 50 cents, throw them in with the cigar box lots. If stamps are on stock pages already, especially if separated by country, you can buyers for lots like that on eBay
. If it's a stock book packed with multiple used copies of classics, even cheap stamps, some collector will want that to search for cancels, color shades or perf varieties. (Among other things, I collect cancels of Austria pre-1918 and Belgian Congo.) If you have entire albums and don't want to go to the trouble of trying to sort and catalogue, you can sell them on eBay
or HipStamp, too -- there are lots of these on eBay
Topicals that are pretty popular: Scouting, sports, Olympics, animals, space, ships/boats, railroad trains. But you might have to spend more time sorting than it's worth to you.
Hope this helps -- good luck!