I want to provide an overview of the material we've written on prayer through the years.
Who should we pray to? Is it acceptable to pray to deceased humans? Or angels? Or should we pray only to God? Is it permissible to pray to Jesus? Or the Holy Spirit?
On praying to the dead, see here, here, and here. And here's a thread in which we had a lengthy discussion with a Roman Catholic on the subject. Steve Hays wrote about the relationship between consulting mediums in Biblical times and praying to the dead today. Two of the most important historical sources on this issue are Celsus and Origen. I discuss some of the relevant evidence from those two sources here and here. And here's a post on Hermas. Here's a post on Abercius. See here regarding Hippolytus. On Lactantius, another important early source, see here. You may want to read through the comment sections of these threads I've linked, since some advocates of praying to the dead posted there, and we interacted with a wide variety of arguments for the practice.
Concerning prayer to angels, see here.
I addressed praying to Jesus and the Holy Spirit here.
Here, here, and here are some articles Steve wrote about how to pray and what we should expect from prayer.
Could our prayers affect the past? What's the relationship between prayer and the future? Steve wrote about praying for the past here and here and praying for the future here.
Steve also wrote about praying within the will of God.
And he wrote about praying for other people here.
Here's a post about publicizing our prayers.
And here's one that addresses, in part, evidence for answered prayer.
Here's a fictional piece Steve wrote about what prayer might look like in the life of a believer.
Peter Pike wrote about Arminianism and prayer here and here. The second article also addresses some common skeptical objections to Christianity related to prayer.
Here's a post Steve wrote about the Mormon practice of praying for confirmation of the truthfulness of Mormonism.