When the Israelites were about to possess their Promised Land, God told them, "Rise up, start your journey and cross River Arnon. I have given King Sihon of Heshbon to you together with his land. Begin to possess it." (Deuteronomy 2:24)
Moses then sent messengers to King Sihon asking him for permission to pass through his territory but King Sihon refused to grant the Israelites permission because God had made his spirit stubborn and his heart obstinate so that He would deliver them into the Israelite's hand. (Deuteronomy 2:30)
God then told Moses, "See I have begun to give King Sihon and his territory to you. Begin to possess it so that you may inherit it." (Deuteronomy 2:31)
From this we can see that God had begun to give King Sihon and his land to the Israelites by making his spirit stubborn and his heart obstinate.
God also wanted the Israelites to do something to Begin to possess it (Deuteronomy 2:31) before they physically fought with King Sihon.
Therefore if God has promised you something or you are standing on one of the Promises of God in the Bible, Begin to possess it (Deuteronomy 2:31) spiritually, mentally and emotionally before you begin trying to possess it physically.
For example if God has promised you a good job,
Begin to possess it Spiritually by praising and thanking Him for it in prayer
Begin to possess it Mentally by believing that God has already given you the job
Begin to possess it Emotionally by feeling that you already have the job.