My wife and I definitely fall under the category of people who travel inexpensively (and therefore frequently).

Once you've arrived at your location of choice the three biggest expenses are usually going to be lodging, food and transportation within the area. If you want to travel more often or for longer periods of time you simply save as much as you can in those three areas.

Transportation:

Avoid taxis, limos and the like and almost always use every form of public transportation available. In larger cities you can purchase all day or multi-day passes that usually save you money. They also give peace of mind about not running out of tokens or accidently riding too far and not having enough to go back the other way or simply being able to joy-ride for a while on the top of the bus in the very front in London, Paris or Hong Kong, etc.

Lodging:

Many options are available depending on your circumstances. My wife and I use Youth Hostels and have been very happy with different ones in NYC, Frankfurt, London, Hong Kong, etc. The time you take to research the choice of Hostel will pay great dividends due to each Hostel being different in clientele, location and amenities.

Food:

Simple, dine out as little as possible (this is really easy for me in Italy and very difficult in Paris). Instead, buy your food from the local markets as much as possible. You can buy ready to eat foods or having an electric immersion heating coil can greatly expand your choices.

Research, research. What I've written is a brief start. There is MUCH more information on the Internet if you'll just look for it. Almost anything you see with words such as youth or back-packing will help and can apply to EVERYONE. Also look at the numerous books at your largest bookstore in the travel section labeled London (or wherever) on X number of dollars a day.

Hope this is a helpful start.

Gregory in Houston