Simple and straight answer: You dont. You can take advice from people in the industry, read forum posts. The decision to join should be entirely your own, and you should understand the risks involved.
But we recommend to do a few acts before investing.
At first verify program status on monitors. Usually, HYIP programs are monitored by some monitors, you need to find its current status like: paying or not paying and read investors comments. Some monitors are dishonest and showing paying status in spite that some programs are paying to monitors only so we recommend to search or open new topic about interesting you program on our Hyip forum. Many members on forum are investing on HYIPs so they will report whether they are scam or not.
Besides you can google program name + scam to see if anybody has been scammed by the program, and "ProgramName" + paying to see if anybody been paid by the program.
If such informations will be not enough we recommend to read basic rules before investing in HYIPs and use Due Diligence methods. Due diligence is the process of investigating a potential investment. It is a way to verify the validity of a particular program.