Who am I to tell God what to do?
God does say to do that very thing. In Isaiah (45:11), He says to "command" Him concerning the works of His hands. It should be noted that the Hebrew verb translated "command" also connotes "conjoining". Or, "helping" maybe? Interesting.
When Jesus said to ask what you will and it shall be done by His "Father in Heaven" (Matthew 18:21), look at it through the lens of the verse in Isaiah. If you want God to do something for you–and I hope I'm not being to forward–make sure beforehand that it's not only in His power, but something that He'd actually do. Does this make sense?
God, make the trees turn bright lavender during the Fall. You said! You said that I could have whatever I wanted and I want lavender foliage on all the deciduous trees in my neighborhood! Do it. What, no "please"? I'm surprised, first of all, that someone so childish would be able to use the word "deciduous" in a sentence correctly. And God rubs His chin. Is there something I'm missing here? Of course, John qualifies the whole process of petitioning God with "according to His will" (1 John 5:14). There you go. But this raises an interesting point. Are we using our imaginations to see God do the outrageous in our lifetime? Paltry. Paltry is the word that comes to mind to define what most people's expectations of what God is able to do. And, yes, God is able to make the trees turn whatever color you want. Of course, He'd have to work around all of the reasons that leaves turn the colors they do. I think it has something to do with photosynthesis and the color spectrum. I don't really know. But even if God did something so cool as that, what are we willing to give Him in return?
Consider this more practical request: "God, make me rich. Please and thank-You." Now that's something I can believe for. But wait. Again with the qualifiers. In Deuteronomy (8:18), there's a very incisive caveat. It says that God will give you wealth "to establish His covenant". In other words, you can't just accrue wealth then do whatever you want with it. It doesn't work that way.
Here's another side of the coin.
Jesus came to this earth to die for man's sin. His sole mission in life. Actually, with reference to the first side, I would say his sole mission was to please His Father, culminating in His death and resurrection. "I only do those things that please the Father" (John 8:29). And upon dying: "it is finished" (John 19:30).
Think of the feeling of invincibility that the disciples had when they were with Jesus. I'm sure they felt they could do anything. But all that power comes with a price. Jesus paid that ultimate price. And thank God He is risen. But with all that was riding on His sacrifice, Peter asked Him (told Him, really) not to die (see Matthew 16:22). That's one request He was unwilling to grant.
"That which thou sowest is not quickened (brought to life) except it die:" (1 Corinthians 15:36)