There are two ways of handling this. I can either sell them on ebay or I can shove them in a bag and take them to my local stamp dealer.
Generally you get more money if you put them on ebay. But they have to be organised. The person who wants stamps from New Zealand probably won't want the ones from Russia. Similarly it helps if they are in sets. Very few people will buy part sets, unless the individual stamps are particularly valuable.
And putting stuff on ebay is time-consuming. You have to scan the items and describe them. And when you sell them, you have to pack them up and post them. And if you don't describe them properly, or if they simply don't arrive, you may have to pay back the money.
So generally, things that are relatively easy to sell I put on ebay. And all the bits and pieces – the schoolboy albums, the tatty first day covers, the bags of loose stamps – go to my local dealer. After all, I simply don't have the time to do handle it all myself.
And what does my dealer do with this lot? First of all, he usually puts it on his shelf, so that potential buyers can riffle through any albums. And then, after a few days, he throws them in a big box and either sells them to smaller stamp dealers or sells them to those firms that advertise in the stamp magazines and offer large chests of miscellaneous stamps. To be honest, I don't really care what happens to the material, as long as I don't have to deal with it.
Here's the latest lot that I sold to a stamp dealer. I got paid £37 for it. There were lot of sheets of Norwegian stamps, a stockbook full of stamps of birds, another of mint French stamps and a large album which had some assorted commonwealth stamps. The reason why I bought the collection, was because there were some nice stamps from Canada and Australia. They're currently sitting in my collection.
See also - Which first day covers are valuable?
Prestige Booklets - are they worth buying?