Amiss

James 4:3
You ask and do not receive, because you ask amiss, that you may spend it on your pleasures.

When we ask for something, are we really asking for a good reason, or are we being selfish? We have all taken advantage of prayer by asking for material things, and although this is not necessarily a bad thing, there are times to ask God for materials, and there times when we should not. If you are praying for a Bible or financial aid, that's not what this verse is referencing. (Unless you plan on spending the money on yourself...) The keyword to whether or not you are praying selfishly is "amiss".
According to blueletterbible.com, the Greek root word of amiss is kakos. One of the three meanings of this root is "miserable, to be ill."*
What does that show you? God doesn't give us the things we ask for because we are asking to be miserable. Of course we don't say "Lord, give me this so that I can be miserable," but He knows what will happen when we get all that we want. God wants to prevent any changes in our attitude and lifestyle that may occur because of material items.

1 John 3:17
If anyone has material possessions and sees his brother in need but has no pity on him, how can the love of God be in him?

If we have so many material possessions, we may no longer see a need for God. We get so caught up in what we still need, that God is totally out of the picture. No longer do we need Jehovah Jireh, our Provider. We can provide for ourselves. But no matter how many things you have, if you forget about your Creator, then you can't feel your purpose in life. You'll wander aimlessly. Have you ever noticed that the poor are often happier than millionaires and movie stars?

James 2:5
Listen, my beloved brethren: Has God not chosen the poor of this world [to be] rich in faith and heirs of the kingdom which He promised to those who love Him?

See? God doesn't care if you have nothing, he has chosen these people to be heirs of his kingdom. I don't know about you, but I would rather be an heir of heaven than pray to be miserable.

*-http://www.blueletterbible.org/lang/lexicon/lexicon.cfm?Strongs=G2560&t=NKJV