The book The Secret is always such a good source of reference when it comes to the Law of Attraction.
Here is a little section of the book that pertains to giving and attracting more money into your life.
"Giving is a powerful action to bring more money into your life.
When you are giving you are saying, "I have plenty."
As you give away money, by the law of attraction,
the Universe opens up and floods money back to you.....mulitplied."
With that being said, make sure that when you give, that it's from a heart that is full of joy and love.
You have to want to give with joy, and the feeling of having more than enough.
If it feels like you are sacrificing, then you will be creating an opposite affect
and will be emitting a signal of lack and not enough.
So basically, if it feels good, then you will be attracting more to you.....if it feels bad, then you will be blocking more coming to you.