How important is preparation to you? 
How about preparation before a summer vacation? 
How about preparation for a business meeting, especially with an important client? 
How about preparation for a big dinner at your house, with out-of-town relatives? 
In all these cases we are pretty serious about preparation. Who, on the day vacation arrives, spontaneously calls everyone to the car as if its a jaunt for ice cream? No one. 
We prepare. We prepare for a new work week. We prepare for a new school year. We prepare for a meeting with new clients and especially old clients. We prepare for a family party. We prepare for vacations. 
Why? Because we want to get the most we possibly can out of these important events. 
It should be easy then for the Christian to see the necessity of preparing for the Lord's Day, especially for the ministry of the Word. 
Is there anything more important to a child of God than meeting with the living God, on the day He ordained, through His appointed means of grace? 
For those desiring to get much out of worship and preaching, preparation will seem the most reasonable duty. It will even be a joyful duty. Joyful because we anticipate God's kindness to give what He promises to all who humbly and earnestly seek Him. "Blessed is the man that heareth me, watching daily at my gates, waiting at the posts of my doors" (Proverbs 8:34).
In two questions of the Westminster Larger Catechism we find an excellent summary of the Bible's teaching on preparation. 
The first is Question 117, which speaks to preparing for the Lord's Day in general:

Q. 117. How is the Sabbath or the Lord’s Day to be sanctified? A. The Sabbath or Lord’s Day is to be sanctified by an holy resting all the day, not only from such works as are at all times sinful, but even from such worldly employments and recreations as are on other days lawful;n and making it our delight to spend the whole time (except so much of it as is to be taken up in works of necessity and mercy) in the public and private exercises of God’s worship: and, to that end, we are to prepare our hearts, and with such foresight, diligence, and moderation, to dispose and seasonably dispatch our worldly business, that we may be the more free and fit for the duties of that day. [scripture support: Exod. 20:8, 10; Exod. 16:25-28; Jer. 17:21-22; Neh. 13:15-22; Matt. 12:1-5; Isa. 58:13-15; Luke 4:16; Acts 20:7; 1 Cor. 16:1; Luke 23:54-56.]

The second is Question 160, which speaks to preparing for the Word to be preached:

Q. 160. What is required of those that hear the Word preached? A. It is required of those that hear the Word preached, that they attend upon it with diligence, preparation, and prayer; examine what they hear by the Scriptures; receive the truth with faith, love, meekness, and readiness of mind, as the Word of God; meditate, and confer of it; hide it in their hearts, and bring forth the fruit of it in their lives. [scripture proofs: Prov. 8:34; 1 Pet. 2:1-2; Luke 8:18; Ps. 119:18; Acts 17:11; Heb. 4:2; 2 Thess. 2:10; James 1:21; 1 Thess. 2:13; Luke 9:44; Heb. 2:1; Deut. 6:6-8; Luke 8:15; James 1:25].

Consider these two practical ways to prepare. First, look up some of the scriptures above provided by the catechism itself. Through them become confident God, not man, speaks of preparation. Only then will your faith work without regret. Second, speak of the Lord's Day to one another at home the way you speak of other big events you prepare for. "The Lord's Day is coming" ... "I am looking forward to this Lord's Day" ... "I am getting this ready so we can have a great Lord's Day." It is not hard to see how the word "vacation" or "family party" fit into those phrases. But should they be the only big events that claim rights of preparation from us and fill our mouths?
Parents, please let me encourage you directly. 
It is your calling to do two things for your children every week to lighten their load as the Lord's Day draws near: (1) pray for them and (2) prepare with them. Pray and prepare like you are praying and preparing for them to come to saving faith in Jesus Christ. It will be no bother to pray and prepare for something so urgent and wonderful and eternal as that! Besides, does not the Lord's Day come with a special promise from God to be a day He acts and works to apply Christ' saving benefits to us and our children? 
So let children learn from the mature about the necessity of preparation. It is the most important meeting of their week. The most important meetings of their lives. Shield them from the spirit of the age which shrugs off great things and foolishly says spontaneous engagement is sufficient for worship. It is not. You know you need your surgeon prepared. You know you need your dentist prepared. You know you need your kid's teacher prepared. You know you need your hotel room prepared. Are you getting salvation from any of these things? No. Then how much more should you want your body, your house, your pastor, your soul prepared for the Lord's Day and that assembly which mimics the final assembly in heaven between the Lord and His redeemed people.