A few excerpts from Introduction to the Devout Life by St. Francis de Sales couldn't hurt anyone, especially these days. I hope to post some on a semi-regular basis as I re-read this classic of Catholic spirituality.
I suppose the best place to start is in the beginning:
You aspire to devotion, dearest Philothea, because being a Christian, you know that it is a virtue extremely pleasing to the divine Majesty: inasmuch as small faults committed in the beginning of any affair, in the progress thereof grow infinitely greater and in the end become almost irreparable, it is necessary before all things that you should know what the virtue of devotion is; for since there is but one true devotion, and very many which are false and vain, if you know not which is the true, you may very easily be deceived, and waste your time in following some devotion which is false and superstitious.
Aurelius was wont to paint all the faces in his pictures to the air and resemblance of the women whom he loved, and each one paints devotion according to his own passion and fancy. He that is given to fasting holds himself for very devout, if he do but fast, though his heart be full of rancour: and though he dare not moisten his tongue in wine or even in water for fear of transgressing sobriety, yet he scruples not to plunge it in the blood of his neighbour, by detraction and calumny. Another will account himself devout, for reciting a great multitude of prayers every day, although afterwards he gives his tongue full liberty to utter peevish, arrogant and injurious words among his familiars and neighbours. Another will readily draw an alms out of his purse to give it to the poor, but he cannot draw any gentleness out of his heart to forgive his enemies. ... even so do many persons cover themselves with certain external actions belonging to holy devotion, and the world believes them to be truly devout and spiritual; whereas in reality they are but statues and phantoms of devotion.
True and living devotion, O Philothea, presupposes the love of God; nay rather it is no other thing than a true love of God; yet not any kind of love; for, in so far as the divine love beautifies our souls, and makes us pleasing to His divine Majesty, it is called grace; in so far as it gives us strength to do good, it is called charity; but when it reaches such a degree of perfection, that it makes us not only do good, but do so carefully, frequently, and readily, then it is called devotion. ... In short, devotion is no other thing than a spiritual nimbleness and vivacity, by means of which charity works in us, or we by her, readily and heartily; and as it is the office of charity to makes us observe all the commandments of God generally and universally, so it is the office of devotion to makes us observe them readily and diligently.