We all know that there is risk in trading, but if we can minimize if then it is good on our side. To reduce risk, one have to understand the maximum money that you can lose on the trade and you should ask yourself if you are willing to accept the lose. Remember, every time a trade is made, a risk is assumed. Therefore, one of the easiest ways to reduce risk is not to over trade.
That doesn't reduce risk at all but rather you're just acknowledging the risk you're taking whenever you trade and when you do that, it goes without saying that you're going to trade only what you can afford to lose. But some prefer doing big trades and they keep looking for that one coin that they can buy early on and then trade for a much higher price.
Reducing the trade amount doesn't necessarily reduce risk. You're just reducing the "risked amount" of money. Some people reduce risk by buying only the coins that just got dumped by the bounty participants. That means you are going to buy at a price lower than the ICO price and then later on sell it for the ICO price (or even higher) once the dump is over. In simpler words, you're going to buy at the dip caused by the crowdsale bounty participants.