"The generous man will be prosperous, and he who waters will himself be watered"
This is the Hebrew word berakah which is usually translated blessing, benefit, gift. The idea seems to be that this is a person who is full of blessings and is constantly blessing people. So the translators decided to use the word generous to convey this idea. This is okay, but it tends to suggest that the person gives away money rather than all types of blessings. There are emotional, spiritual, physical, mental, relational, financial, and many other kinds of blessings. It is the person who is looking to bless others that is being talked about here in this proverb.
This is the Hebrew word nephesh which means soul. This is the word for the invisible interior part of a person's life. It is your soul that you are trying to add to through the acquiring of wisdom. You are trying, as Moses says in Psalm 90, to present a soul full of wisdom to the Lord at the end of life.
In this case Solomon is saying that it is the person who is always ready to bless others in some way who will have the enlarged soul.
This is the Hebrew word dashen which means to be fat or grow fat. The idea is that one has abundance or over what is needed. The way that the Hebrew mindset conveyed this was through being fat. The person who was overweight had abundance. In fact, in their culture this was a somewhat desirable thing. We see this idea expressed in the movie Fiddler on the Roof when the main character sings that he dreams about having a proper double chin.
Remember that this is not being applied only to the physical body but metaphorically to the whole of life through the application to the soul. You want a fat soul, laden with wisdom and blessings to give away. The more you give away blessings to others, the more your soul will be enlarged and prosper.
The danger with this translation of the proverb is that it makes it seem to be about money and financial areas. This is, however, not what it is about. It is about becoming a better person with an outward focus towards others and seeking to meet the needs of others. This verse is a different way of saying what Jesus said when he said, “Thou shalt love thy neighbor as thyself.” Giving a blessing is looking for a need, an encouragement, or a want that you can give to another person. It is an outward focus rather than a selfish one.
This is the Hebrew word ravah which means to be saturated or drink one's fill, to drench, satisfy. The idea is the same as the first phrase in this proverb but spoken from a different angle. If you seek to satisfy the needs and concerns in others, you will increase the needs that are met in your life.
This outward focus is the way life works. Let me add what is not spoken in this proverb. This is a general rule of thumb. There are people who, no matter how much you meet their needs, their selfish leech-like parasitic thinking knows no end. These people are the exception to these verses and will suck you dry if you try and fill them up. They have psychological dysfunctions that do not allow them to live out the truths of this verse. They would have you give and give until you disrespect yourself in the amount you give to them. Do not do this. Their behavior is covered by other proverbs. I say that so that you do not think that this verse is not true because you found a person in your life where it does not work. It works as a general rule, but there are people who are so self-focused and/or damaged that they are an exception to this verse because of their selfishness or victimization.