There are a number of things that those new to stamp collecting wonder about. Sometimes it seems that the world of philately is a castle with a moat around it, as stamps may be easy to come by, while information about them is at a premium. Literally.
But collectors new (and otherwise) always want to know several things:
What areas are "good" to collect? They usually mean what stamps are more highly valued and will maintain their value over time. (New collectors may ask which are "good investments," unaware that investing in stamps entails much more than just buying them.) The wise answer is to send them on their way to: compare stamps using eBay search; get a catalog and prices realized from a worldwide stamp auction to see what sold best; look at a basic reference catalog like Scott's or Gibbons for prices. If possible find a number of years of the catalog to chart the movement of the prices.
Where do I find stamp dealers for the type of material I want to collect? Stamp dealers have gone online. From the smallest kitchen table dealer to the largest retail and auction dealers stamps are to be found via the Internet in 2012. A disadvantage is that you can't see the stamp in person. Yes, high definition scans can let you see the stamp close-up, but hidden flaws (repaired tear, washed cancel, etc.) can only be revealed by forensic testing. That may sound like overkill, but when you're paying hundreds of dollars for a stamp you want to be sure that it is what it seems to be.
What's the best way to invest in stamps? Any investment includes risk. So the first thing to consider is minimizing risk by buying only solid areas. And only in the finest condition. Again, classic U.S. has held values over the years. Pre-twentieth century classic worldwide with a proven record is a safe area. China is a good investment, but how long will that be true? It has gone up so much recently that one wonders if there is still enough upside to make it a good place to put your investment funds.
Classic airmail stamps have held their value, but on the other hand, postal history that is airmail related in many cases has hit a wall of lack of interest from new, mostly younger collectors. Although common items like basic zeppelin covers are offered at higher prices, the prices are inflated by unknowledgeable or even greedy unprofessional sellers. In truth, classic pioneer flights of the early part of the 20th century may be a good place to put some of your stamp funds, although, again, the risk is that younger generations don't have the same interest in airmail as previous ones. Lack of demand will mean falling of prices.
Stamps are now graded, like baseball cards. Starting in the 90's baseball card manufacturers threw everything, including the kitchen sink into their cards. (Almost: actual pieces of stadium seats and the like were embedded in the cards.) It was overkill. Part of the scene was the grading of baseball cards, which, if you could get a good grade (i.e. 9.5 +) on your card (which now resided inside of a plastic slab) your previously $3 card was magically turned into a $50 or better card. The fever hung around this scene for a number of years, before prices for graded cards settled back down to earth.
Now stamps are part of the grading trend. Or more correctly, they are currently part of a trend that was a big deal a few years ago, but has fallen into disfavor with the collecting community. Of course, things go up and down in the collecting/investing world. Perhaps in some future date stamps inside big slabs of plastic with a grading mark on them will be all the rage. But currently, these "investment grade items" don't look like such good investments.
But the short answer to the question "What should I collect?" is collect what you like. And how to find out what you like is to a) subscribe to a good philatelic periodical like Stamp News b) peruse a worldwide stamp catalog like Gibbons or Scott c) go to a stamp show to expose yourself to stamp culture d) join a stamp club (you can quit if it does not fit). Through all this you'll be learning about stamp collecting as well as yourself. And like the man said, knowledge is power.