My strategy is to buy coins when the price drops sharply.
Sometimes I fail, because the price drops more than I expected.
But, to prevent this worse situation, I put 30% of my budget at the time of initial investment.
If the price getting down again, I put 30% more.
With this strategy, I am getting some money so far.
In conclusion, I recommend you guys to buy coins when they drops rapidly.
After sharp drop, there should be sharp rising.