I would, therefore, advise you to pursue a regular plan of written exercises.  This will be very easy, if you only learn to think methodically.  Select, chiefly, practical subjects; which your Sabbath-school lessons, your subjects of meditation, and your daily study of the Scriptures, will furnish in great abundance.  The principal reason why young persons find this exercise so difficult is, that they usually select abstract subjects, which have scarce any relation to the common concerns of life.  On this account, it will be greatly to your advantage to choose some Scripture truth as the subject of your exercise.  The Bible is a practical book, and we have a personal interest in everything it contains.  When you have selected your subject, carefully separate the different parts or propositions it contains, and arrange them under different heads.  This you will find a great assistance in directing your thoughts.  If you look at the whole subject at once, your ideas will he obscure, indefinite, and confused.  But all this difficulty will be removed, by a judicious division of its parts.  Set apart regular portions of time to be employed in writing.  Let these seasons be as frequent as may consist with your other duties, and observe them strictly.  Do not indulge the absurd notion that you can write only when you feel like it.  Remember your object is to discipline the mind, and bring it under the control of the will.  But, to suffer your mind to be controlled by your feelings, in the very act of discipline, is absurd.  As well might a mother talk of governing her child, while she allows it to do as it pleases.  Finish one division of your subject every time you sit down to this exercise, until the whole is completed.  Then lay it aside till you have finished another.  After this, review, correct, and copy the first one.  The advantage of laying aside an exercise for some time, before correcting it, is, that you will be more likely to discover its defects than while your first thoughts upon the subject are fresh in your mind.  But never commence a subject, and leave it unfinished.  Such a course renders the mind fickle, and unfits it for close study and patient investigation.  Finish what you begin, however difficult you may find it.  Scarce any habit is of more practical importance than perseverance.  Do not be discouraged, even if you should be able to bring forth but one idea under each division of your subject.  You will improve with every exercise.  I well recollect the first attempt I made at writing.  With all the study of which I was capable, I could not produce more than five or six lines.  Carefully preserve all your manuscripts.  By referring to them occasionally, you will discover your progress in improvement.  In these exercises you can make use of the knowledge you acquire in reading, whenever it applies to your subject.  But, in everything, remember your dependence upon God, and seek the direction of his Holy Spirit.