Investment in postage stamps should not really be called collecting since the real meaning of the word collecting is to obtain as many of a thing as you possibly can, and investment buying of stamps is something entirely different. Actually, investment buying is something that only people who have a surplus of cash can do.
Unless you are so financially situated, investment buying is not for you. The best you can do is to buy a few stamps now and then and hope for the best. The real investment buyer follows every item of news in every periodical devoted to stamps. He is up on world trends, politics in particular, since political changes in countries profoundly affect the value of its postage stamps.
Investment buying takes two forms. One is the accumulation of stocks of current stamps, usually in full sheets, and in quantities of those sheets. The other is buying rare and costly items, holding them until they rise higher, and then selling them at a profit.
Investment buying of postage stamps is a good hobby and a good way to make a buck if you are already rich. It is a good way to lose your shirt if you are not rich enough to play with a lot of money, or if you don’t know all the ins and outs of philately.