Answer (short) –

1. In sadness, hold on to Krishna more strongly. When a boat is attached to a heavy anchor, the anchor minimizes the shaking of the boat in the midst of strong waves.

2. Engage yourself in an activity which is positive, purposeful, and constructive. This will take away your mind from the source of sadness.

3. At a practical level, do the needful to deal with the problems which are causing distress or sadness.

4. Most important to regularly chant the holy names of the Lord – Hare Krishna Hare Krishna Krishna Krishna Hare Hare | Hare Rama Hare Rama Rama Rama Hare Hare||

Answer (long)-  When we are in a boat and constant waves are coming, we cannot avoid the restlessness that is going to come due to the waves, but if the boat is anchored to some heavier object then the boat will shake less.

In life we will go through waves of dualities, sometimes happiness and sometimes distress. There may be phases when distress will come more and more. Based on our karmic situation in life we may go through phases where difficulties may be more and at that time sadness may seem to recur more and more. At such time we need to hold Krishna stronger because Krishna is our anchor. Everything else in this world is temporary- tāṁs titikṣasva bhārata (BG 2.14) – Arjuna, you should tolerate this because āgamāpāyino ’nityās, (BG 2.14) everything in this world is temporary. To the extent we recognize that the world is temporary, to the extent we will not get overwhelmed by it. Whatever distress we have right now, we should know that it is not going to last forever.

Suppose we are going in a train and we come to a particular station where people are nasty, there is foul smell, everything is dirty etc. But the train will eventually move out of that station. If we continue to stay mentally in that station thinking “why was it so bad” etc. then we will be causing ourselves distress. If we also move ahead with the train, don’t allow our mind dwell on that station then we will not be so troubled by it.

Similarly in our case when we face distress, what we can do is that rather than our mind stay with the source of that distress, we need to do something positive, constructive, and purposeful. Especially find out some activity in which we can absorb ourselves then mind will not be able dwell on the sources of sadness. That way we can minimize the sadness.

To summarize, first we focus on Krishna, second we focus on striving to find some constructive activity in which we can keep ourselves engaged. And at the practical level we need to the needful to deal with the problems that are source of sadness.
Read more http://www.thespiritualscientist.com/2016/12/can-cope-enduring-sadness/