It is important to track sentiment indicators and volume (up/down) is one that can provide us with clues as to what investors are thinking. I like this particular chart that we watch regularly to help discern the daily preferences and the extent of buying and selling pressure.
Notice that on the down days we see a much greater (and somewhat wider) red indication. Throughout this recent market cycle, that has been a regular occurrence. It appears that investors are much more likely to sell with real conviction on the day with a downward bias.
In fact, when we look at the hourly levels, we notice that the days that are positive, usually have a down segment and those also show higher volume levels. This is a good way to start to build on a trend change. For now, generally, the bulls are still in charge.