One of C.S. Lewis's enjoyable reads is his Screwtape Letters, a collection of "letters" written by a senior demon to his understudy, his nephew demon. These letters are instructions of how to seek to undermine the effectiveness of the nephew's Christian "patient." You can purchase the book here, and a nice dramatized version by Focus on the Family here.
Letter four is about prayer. Notice how Lewis portrays Satan's desires in the believer's prayer life.
"The best thing, where it is possible, is to keep the patient from the serious intention of praying altogether. When the patient is an adult recently reconverted to the Enemy's party, like your man, this is best done by encouraging him to remember, or to think he remembers, the parrot-like nature of his prayers in childhood. In reaction against that, he may be persuaded to aim at something entirely spontaneous, inward, informal, and unregularised; and what this will actually mean to a beginner will be an effort to produce in himself a vaguely devotional mood in which real concentration of will and intelligence have no part" (p16-17).
Satan does not mind us praying, as long as our prayers are not serious, sober, and concentrated. It is good and necessary for the Christian to devote serious time to serious prayer.
"If this fails, you must fall back on a subtler misdirection of his intention. Whenever they are attending to the Enemy Himself we are defeated, but there are ways of preventing them from doing so. The simplest is to turn their gaze away from Him towards themselves. Keep them watching their own minds and trying to produce feelings there by the action of their own wills" (p17).
Satan does not mind us praying as long as the focus of our prayers is on self, and not truly on the Lord. When our prayers become so humanistic, materialistic, and narcissistic in nature, Satan does not mind those prayers at all.
"But even if He defeats your first attempt at misdirection, we have a subtler weapon. The humans do not start from that direct perception of Him which we, unhappily, cannot avoid. They have never known that ghastly luminosity, that stabbing and searing glare which makes the background of permanent pain to our lives. If you look into your patient's mind when he is praying, you will not find that. If you examine the object to which he is attending, you will find that it is a composite object containing many quite ridiculous ingredients. There will be images derived from pictures of the Enemy as He appeared during the discreditable episode known as the Incarnation: there will be vaguer - perhaps quite savage and puerile - images associated with the other two Persons. There will even be some of his own reverence (and of bodily sensations accompanying it) objectified and attributed to the object revered. I have known cases where what the patient called his 'God' was actually located - up and to the left at the corner of the bedroom ceiling, or inside his own head, or in a crucifix on the wall. But whatever the nature of the composite object, you must keep him praying to it - to the thing that he has made, not to the Person who has made him." "For if he ever comes to make the distinction, if ever he consciously directs his prayers 'not to what I think thou art but to what thou knowest thyself to be', our situation is, for the moment, desperate" (p17-18).
Satan does not mind us praying as long as we don't think biblically about our God. In your prayers, have such high and biblical thoughts of God that He consumes your prayers.
Believers must pray; but it matters how we pray. Pray in such a way to make Satan tremble.