We don't practice market timing at the CEF/ETF Income Laboratory (and our portfolios did fall with the rest of the market in March) but there is a surefire way of increasing your margin of safety with your closed-end funds investments if/when a bear market does hit.
The simpler answer is: avoid overpriced funds! Especially if there is a less overvalued alternative available from the same sector. CEF premium/discounts can often vary wildly based on no discernible reason other than imbalanced supply and demand, and the nimble investor can rotate out of these to save money