A good hold of your personal feelings would definitely allow to better read someone else's emotions.
Once you are able to do that, you find yourself in the position of influencing the that person feels.
Why would you want to influence someone? You may intend this in order to convince them about the qualities and virtue of an idea, product, concept or project.
In other cases, your influencing other persons' emotions contributes to their own good.
The fact that you love or appreciate someone sometimes stirs up in you the intention of changing their behavior for their benefit.
A depressed or angry person can be put in a better frame of mind if you know how to efficiently influence her state and, thus, can engage in some cooperative activity.
However, the major benefit of your handling other persons' emotions resides in a better understanding of the respective individuals.
An improved connection results from this instance, as you are thus enabled to empathize with them and act accordingly.
Therefore, if you understand the other, you will know that, if he/she is in a bad mood, you then have to leave them alone, offer a cup of tea or coffee or talk to them.
An appropriate reaction towards somebody's state is a good way of helping them.
The basic premise when attempting to influence someone is to be allied with that person as any antagonizing or hostile gesture will make her less cooperative and less willing to listen to you.
Having common interests sure smooths the way.
A golden rule is the one according to which you get what you give.
Consequently, being nice and doing good to a stranger will bring about a similar occurrence in your life.
Reciprocity is a thing you cause to happen.
Let us take a simple example.
If you go to a bar and buy a round of beer to the house, without expecting to be reciprocated, your act of kindness is very likely to be rewarded.
The ones that benefited from your gentle gesture will somehow spread the word and you will be treated nicely in the future.
But you sometimes don't want to be considered an easy-to-be- taken-advantage of kind of person.
Hence the question "How do I know when to be nice and when to be though?" appears.
Based on the saying "You attract more bees with honey than with vinegar", one can generalize that being nice pays more dividends.
On the other hand, here are some situations when you are likely to be more effective if being tough:

• when you want to stop an acquaintance from making inappropriate jokes on issues that you take seriously;
• when someone is trying to take advantage of you, for example during a negotiation.
  

However, toughness has to be used moderately.