A few strategies can stand out on what to do during periods when cryptocurrency markets are in decline:

1. **Thinking Like Stocks**: It is important to think about your cryptocurrency investments long-term. Short-term fluctuations can be frustrating, but from a long-term perspective, dips can be considered buying opportunities.

2. **Research and Information**: Follow market news and analyst comments to understand the reasons for market declines. Declines are often tied to market-wide sentiment and external factors.

3. **Portfolio Diversification**: Spreading your investments across multiple projects, not just one cryptocurrency, can reduce your risk. You can also consider investing in other investment instruments other than crypto, such as stocks and commodities.

4. **Not Selling in a Panic**: Fluctuations in the market are natural. Instead of panicking and selling at a low price, it may be more logical to wait strategically or make additional purchases at points you deem appropriate.

5. **Technical and Fundamental Analysis**: Performing technical analysis of cryptocurrencies (examining charts, support and resistance levels) and evaluating the long-term potential of projects with fundamental analysis can help you make informed decisions.

6. **Use of Stop-Loss**: In terms of risk management, placing an automatic sell order (stop-loss) at a certain level can help prevent large losses.

Every investor's risk tolerance and investment goals are different. It's important to seek expert advice and do your own research, taking into account your own financial situation and objectives.