3. Be careful to form good HABITS.
Almost all permanent habits are contracted in youth, and these do in fact form the character of the man through life. It is Paley, I believe, who remarks that we act from habit nine times, where we do once from deliberation. Little do young people apprehend the momentous consequences of many of their most frequently repeated actions. Some habits are merely inconvenient, but have no moral quality; others affect the principles of our conduct, and become sources of good or evil to an incalculable degree. As to the former, they should be avoided, as detracting from our comfort and ultimately interfering with our usefulness; but the latter should be deprecated, as laying the foundation of a wicked character, and as standing in the way of all mental and moral improvement.
– Archibald Alexander; Counsels of the Aged to the Young (See here for more info)