The best simplest advice I have heard is "don't ever lose money".

As silly and simple this may sound, we are all guilty of some rash decisions. Some maybe even gamble a lot or invest in poor timing, invest in future options and so forth.
Some of those may sound like a good option especially investing in future options but the thing I learned is future is unknown and cannot predict the value of your investment. Be safe and invest reasonable amount so you don't lose a substantial amount of money or don't at all invest and wait for that industry to mature and then invest knowing all the while its prospects.