Sacrificial giving

2 Corinthians 9:8
“And God is able to make all grace abound toward you; that ye, always having all sufficiency in all things, may abound to every good work.” KJV
Another action that is necessary in someone believing for abundance is Tithing. You cannot say you believing God for abundance and you do not want tithe, for this simple reason:

Malachi 3:10-11
“Bring all the tithes into the storehouse so there will be enough food in my Temple. If you do," says the Lord of Heaven's Armies, "I will open the windows of heaven for you. I will pour out a blessing so great you won't have enough room to take it in! Try it! Put me to the test! Your crops will be abundant…” NLT

“Bring the full amount of your tithes to the Temple, so that there will be plenty of food there. Put me to the test and you will see that I will open the windows of heaven and pour out on you in abundance all kinds of good things.” GNT

When you tithe, you recognize God as your source, and God who is your source is a God of abundance. By tithing you are expressing your faith toward God for abundance also, this is because at the root of someone not tithing is fear of insufficient funds. Tithing is a faith action. The believer who does not tithe is already contradicting his faith. He will not experience abundance.

Another action that can invoke abundance is SACRIFICIAL giving. God Himself exemplified this in giving Jesus to be sacrificed for mankind. He did it so that he can have many sons.
“In bringing many sons to glory, it was fitting that God, for whom and through whom everything exists, should make the author of their salvation perfect through suffering.” 
Hebrews 2:10 NIV

When Abraham gave up Isaac, God swore to him and said, “in blessing I will bless you and in multiplying I will multiply you”, sacrificial giving moves the hand of God to bless abundantly.