Many of us have been given messages throughout our lives that have caused us to believe a desire for prosperity is selfish (or there is nobility in lack - like the Biblical idea it is much easier for a camel to go through the eye of the needle than for a rich man to enter the kingdom of God). Others may believe on some level they are not deserving of prosperity. I know I have struggled with both of these beliefs throughout my life. However, in order to truly be in a position to help others, we must first be in a position to help ourselves. Prosperity doesn't mean keeping everything for yourself. The more prosperous you are in all ways, the more you have to share with others. At the same time, it's okay to want things because you want them. There is no shame in desire. Desire does not have to equal greed, and you can choose to be a good steward of your prosperity so it doesn't cross the line into avarice.
If you believe - even on a deeply subconscious level - it is not okay to want "things" for yourself, then your thoughts, words, and actions won't align in a way that allows the universe to consistently deliver for you. Therefore, the first step in changing your mindset about prosperity is to notice thoughts that are counter to being prosperous as soon as they arise. Often, these thoughts are quite fleeting or just feel normal. So the first step in changing your mindset about prosperity is to listen deeply to your thoughts and words. Do you have thoughts or beliefs that are limiting what the universe provides?
Thought, word, and action are all creative. In other words, thoughts become things. The things we say, think, and do send messages to the universe, which then creates the exact conditions we have requested through our thought, word, and deed. So every time we think a limiting thought about prosperity, the universe responds in kind, giving us what we have created.
When you catch yourself thinking a limiting thought (or speaking of limitation) about prosperity, it is important to realign that thought (or word or action) right away. Here's a concrete example. You might catch yourself saying or thinking, "I'm broke!" Catch that thought and immediately cancel and replace it. When you hear this come out of your mouth (or pass through your brain), say to yourself (it can be in your head - doesn't need to be aloud), "Cancel that. I am prosperous. I have all I need to live the life I choose for myself," or something similar.
The point is to make it a positive statement that cancels out the negativity that passed through your mind. You don't even have to believe this to be the truth. You've probably heard the old saw, "Fake it 'til you make it." Changing your thoughts at first may seem unnatural, but consistent effort eventually brings a change in beliefs, attitude, and ultimately circumstances.