Making Money the Old-Fashioned Way
The most popular and probably the steadiest way to make cash in Guild Wars is from faction farming. To do this you go to one of the new player cities, gather a good long mission and head into it by yourself or with some friends. You can spend all day going back and forth, traveling across your instance, collecting treasure and a nice reward at the end. You can even spice this up a bit if you get a Tier 1 salvage kit, which lets you you get more treasure to sell at the end of each trip.
The Service Industry
Guild Wars has a lot of very rich people who do not like to travel back and forth. Couriers can make several thousand gold an hour by running items back and forth or providing an escort for low level alts. Make sure you always get at least half of the agreed upon amount up front. You can maximize your business by sitting in the new player areas and announcing in general chat that you are making a popular run, like from Beacon to Forge, and grab several people or items at once.
Market Trader
This is somewhat similar to the courier, but in this case you take advantage of the fact there is no centralized market hub in Guild Wars. You find an item in high demand, buy it near where it drops at a steep discount, then bring several copies of that item to new player cities and sell it for 400 to 500 percent price increase. Dyes are very popular for this, especially black.