Thomas Manton in his sermon on 1 Thess. 5:17 (pray without ceasing) defines prayer as desire

“It is an offering up of our desires. Desires are the soul and life of prayer, words are but the body. Now as the body without the soul is dead, so are prayers unless they are animated with our desires: Ps. 10:17, ‘Lord, thou hast heard the desire of the humble.’ God heareth not words, but desires.”

He then further specifies the nature of this offering up of prayer.

First the desire is offered with the right heart.

“These desires are offered unto God, or brought before the Lord in this solemn way: Zeph. 3:10, ‘My suppliants, even the daughters of my dispersed, shall bring mine offering;’ that is, shall reverently express their desires to God. An offering was either a sacrifice, and prayer is a spiritual sacrifices: 1 Peter 2:5,”

The prayer is offered up not on our own account but we come bearing Christ’s name

“They are desires presented in the name of Christ, in whom alone we are acceptable to God: John 16:23, ‘Whatsoever ye shall ask the Father in my name, he will give it you.’”

Finally these are agreeable to God

“All our desires must be regulated by his revealed will, and subordinated to his secret will, so far as God seeth it fit for his glory and our good; for upon other terms he is not bound to us.”