Most REIT's specialize in a certain segment, which you can find in the fund summary. Understand the risks of each sector. For example, REIT's holding undeveloped land carry more risk than REITs investing in high-end apartments in a major metropolis.
REIT's should pay a dividend from operations. At times, REIT's use the additional capital to fund dividends due to stressed assets.
Timing the investment in real estate is the key to making money. If REIT was created after a housing market recession; it could own and buy valuable properties at low prices.