There are some basic "rules" which are good to know, before you invest in HYIPs:
Never invest more than you would like to lose;
Do not invest anything before you have read, read and read some more about the different programs and strategys;
I recommend that you read in the forums. Preferably more than one, I read about 5 or 6;
Do not trust all monitors that much. Try to find only honest monitor services. Some admins of hyip monitors are admins of monitored hyip programs also. Huge part of monitors announcing "Paying" long after ordinary members reports "non paying";
Be aware of duplicates, scammer scripts. It is easy to set up a HYIP buying a script - all too easy. Do not trust hyip programs structured on pirated scripts;
Avoid HYIPs with unrealistic returns. "25% a day for 6 days" would be a scam. Remember that Saturday and Sunday are non-trading days;
Diversify your investments - do not put all your eggs in one basket;
When you consider to join a certain HYIP, google it with "ProgramName" + scam to see if anybody has been scammed by the program, and "ProgramName" + paying to see if anybody been paid by the program;
Always base your opinion on your own Due Diligence, never base it on a single persons recommandation;
Take your pricipal out ASAP, and then invest with the house''''s money;
Try to choose brand new programs to invest. Even if the chosen program turn to be scam or ponzie you have still chance to be in profit;
The problem with most of the programs up now, is that they have no legitimate way of earning income for their depositors, they just use future deposits to pay the ROI on past deposits. The rule is that if they offer more than 10% or 12% daily you can expect that it will not last very long.
Some of these sites will tell you up front that they are hyip games, and if you lose, they are not responsible for paying you back. Many of these sites will offer up to 300% daily ROI on your deposits, and these are the riskiest, and is mostly like gambling.