Johannes G Vos wrote a commentary on the Westminster Larger Catechism, one of a very few works which deals with this document specifically. (The Shorter Catechism is much better known and studied, even though it was seemingly originally intended as a more elementary form of the same teachings.) In dealing with the question in the Larger Catechism on the duty of Christians after they have received the sacrament of the Lord’s supper, Vos draws these points out of the answer in the catechism itself.
1. … Since the Lord’s Supper is intended to bring real spiritual benefit to Christian people, it is their duty to consider seriously how they have conducted themselves prior to and at the sacrament, and what benefit they have received. To drop the matter from our thoughts as soon as the actual communion service is dismissed would be to lose a part of the spiritual profit that we should receive from the sacrament.
2. … While it is undoubtedly true that most serious Christians consciously experience benefit at the time [when the sacrament is received] and immediately afterwards, this is not always nor necessarily the case. Sometimes God in his wisdom withholds the blessing, or the consciousness of the blessing, for a time. As in the case of baptism, the benefits of the Lord’s Supper are not tied or limited to the time of administration.
3. When benefit is experienced, [this should produce the following attitudes in the communicant:] (a) An attitude of thankfulness to God; (b) a prayerful desire that the blessing may be continued; (c) a careful avoidance of pride or overconfidence which would occasion a relapse into sin; (d) a sincere purpose of paying his [or her] vows to God; (e) a desire to partake of the Lord’s Supper often. The danger of spiritual pride or overconfidence is especially to be guarded against. The Christian who has experienced spiritual blessings and benefits is always in danger of becoming overconfident and starting to trust in himself instead of in Christ. This will lead to a humiliating fall into sin unless carefully guarded against.
4. When no immediate benefit is experienced [the Christian] should realise that the failure to experience spiritual benefit may be his own fault, and therefore he should review his preparation for, and conduct at, the sacrament. If he finds himself to be at fault in either of these matters, he is ‘to be humbled, and to attend upon it afterward with more care and diligence.’ That is to say, lack of proper preparation for the Lord’s Supper and improper partaking of the sacrament are sins, and should be repented of the same as any other sins.
5. [If a Christian] is not conscious of benefit received from the Lord’s Supper, but does not find this to have been caused by his own faults … [he or she] should ‘wait for the fruit of it in due time;’ that is, his attitude toward God in connection with this matter should be an attitude of faith, confidently expecting a blessing, and an attitude of patience, being willing for the blessing to be deferred if that is God’s holy will. There are many examples in the Bible of saints whose blessings were deferred, either to develop their faith or because of some secret purpose of God. Impatience is always contrary to faith.
This is all based on the answer to question 175, but the section on the Lord’s supper starts at question 168 in the Larger Catechism (the section on the sacraments in general stretches from q161-177) and the material it contains is very useful, not just doctrinally but from a practical point of view too – the catechism as a whole is a very pastorally-oriented document, intended for ordinary Christians to make use of.