Your instruction would've been great if you didn't make a huge mistake. Obviously, you must've meant buying low and selling high.
Anyway, I think that the idea is good, but can be specified a bit. To invest safely one has to follow these steps:
1. Look at top 20 coins on coinmarketcap.
2. Define those which dropped 20%+.
3. Look at the news about these coins to make sure the drop is not due to serious problems discovered.
4. Look at the price chart of the coin and make sure it's price was 20%+ higher than now for at least two weeks.
5. BUY IMMEDIATELY those coins which met all the requirements.
6. Wait till the price recovers, then watch the price carefully once per hour.
7. Sell when it drops 5% from the maximum you saw that day.