Prayer is talking to that unknowable being/energy/consciousness, whatever you want to call it... God.
It's better to be done with true selflessness & faith... & that unknowable being/energy/consciousness ALWAYS hears them & ALWAYS answers them.
But ask yourself, not WHAT are you praying for... but WHY...
If what you're praying for stems from a place that only helps SELF then no, it will not be given... if what you pray for is to help self help others then it is ALWAYS given.
For example... at one point in my life I was short $4,000 for me & my roommate at the time & we were about to get evicted. I wouldn't have cared to be homeless because I accept all that comes with my life but I understood my roommate did not have the same relationship I have with God & so I prayed for help, because it would've broken them & the very next week through what some would call crazy coincidences I came up on $4,000 EXACTLY, the day that we would've been homeless ended up being the day we moved into a brand new & much nicer apartment. All within the same week.
I speak to God no different than speaking to a Parent... as if in the same room... that is the level of relationship it desires to have with every one of its children.
WHY do you pray? For selfish desires? For others? To get yourself out of a jam so you can further continue a sinful lifestyle or so you can become closer to your Source? WHEN do you speak to God? Do you speak to God as often as you would speak to a family member or best friend? Or do you only speak to God when you NEED something?
Symbolically speaking... a lot of people thank God for things the Devil helped them achieve. Knowing the difference when what you've done comes from a place of Good from a place of Self will undistort how Prayer works in the eyes of many if they chose to pay attention.
The reason Prayer doesn't work for many is because there is no true belief behind it... & God cannot be mocked.
If you Pray without TRUE faith, you might as well have remained Silent...