Diversification, market knowledge and development in the past is the key to success
How to invest
Here are some ideas, what is important to focus on when buying postage stamps as an alternative investment. As I try to use my profesional business knowledge also in collecting, I stick to the following rules:
Do Not Overpay
Buy thoughtfully and know the real value before you pay.
Quality Is the Key
Focus on quality, rare and well-verified stamps.
Diversify
Spread your investments across countries, periods and collections.
Networking with Other Philatelists and Experts
Share experience and verify information with experts.
Sell Anything You Do Not Need
Don't let stamps sit idle -- sell what you no longer need.
Buy When the Market Is Low, Sell When the Market Is High
Use market price swings to your advantage.

Following these rules, I have managed to keep the costs under control and if I would like to sell my collection, I will make a nice profit on it, because I know where and how to sell it as well as who might be the right potential buyers.
“Warren Buffett: it's no coincidence that the 'world's greatest investor' is also a seasoned philatelist...”Source: Read the original article