According to Śrīla Rūpa Gosvāmī, there are six impediments to the discharge of devotional service, and also six activities favorable to progress in devotional service.
The first impediment is atyāhāra, overeating or accumulating more wealth than we need. When we give free rein to the senses in an effort to enjoy to the highest degree, we become degraded. A devotee should therefore eat only enough to maintain his body and soul together; he should not allow his tongue unrestricted license to eat anything and everything it likes. The Bhagavad-gītā and the great ācāryas, or spiritual masters, have prescribed certain foods for human beings, and one who eats these foods eats in the mode of goodness. These foods include grains, fruits, vegetables, milk products, and sugar—and nothing more. A devotee does not eat extravagantly; he simply eats what he offers to the Supreme Lord, Kṛṣṇa. He is interested in kṛṣṇa-prasādam (food offered to the Lord) and not in satisfying his tongue. Therefore he does not desire anything extraordinary to eat.
Similarly, a devotee does not wish to accumulate a large bank balance: he simply earns as much as he requires. This is called yāvad-artha or yuktāhāra. In the material world everyone is very active in earning more and more money and in increasing eating and sleeping and gratifying the senses; such is the mission of most people's lives. But these activities should be absent from the life of a devotee.
The next impediment Śrīla Rūpa Gosvāmī mentions is prayāsa, endeavoring very hard for material things. A devotee should not be very enthusiastic about attaining any material goal. He should not be like persons who engage in fruitive activities, who work very hard day and night to attain material rewards. All such persons have some ambition—to become a very big businessman, to become a great industrialist, to become a great poet or philosopher. But they do not know that even if their ambition is fulfilled, the result is temporary. As soon as the body is finished, all material achievements are also finished. No one takes with him anything he has achieved materially in this world. The only thing he can carry with him is his asset of devotional service; that alone is never vanquished.
The next impediment to devotional service is prajalpa, talking of mundane subject matter. Many people unnecessarily talk of the daily happenings in the newspapers and pass the time without any profit. A devotee, however, does not indulge in unnecessary talks of politics or economics. Nor is a devotee very strict in following ritualistic rules and regulations mentioned in the Vedas. Becoming enamored of these rituals is the next impediment, called niyamāgraha. Because a devotee fully engages in the supreme service of the Lord, he automatically fulfills all other obligations and doesn't have to execute all the details of Vedic rituals. As the Śrīmad-Bhāgavatam (11.5.41) says,
na kiṅkaro nāyam ṛṇī ca rājan
sarvātmanā yaḥ śaraṇaṁ śaraṇyaṁ
gato mukundaṁ parihṛtya kartam
"Every human being born in this world is immediately indebted to the demigods, the great sages, ordinary living entities, the family, society, and so on. But a person who surrenders unto the lotus feet of the Lord and engages fully in His service is no longer indebted to anyone. In other words, he has no obligations to fulfill except executing devotional service."
Finally, a devotee should not be greedy (laulyam), nor should he mix with ordinary materialistic men (jana-saṅga).
These are six negatives, or "do-nots," for the devotee; therefore one who wants to attain the perfectional stage of love of Godhead refrains from these things.
Similarly, there are six positive items for advancing in devotional service. First, while one should not be enthusiastic to attain material achievements, one should be very enthusiastic to attain the perfectional stage of devotional service. This enthusiasm is called utsāha. A living entity cannot stop acting. So when he is forbidden to become enthusiastic about material achievements, he should at once be encouraged to be enthusiastic about spiritual achievements. Enthusiasm is a symptom of the living entity; it cannot be stopped. It is just like a powerful engine: if you utilize it properly, it will give immense production. Therefore enthusiasm should be purified. Instead of employing enthusiasm for attaining material goals, one should be enthusiastic about achieving the perfectional stage of devotional service. Indeed, enthusing His devotees in devotional service is the purpose for which Kṛṣṇa descends to this material world.
The next item favorable for devotional service is niścaya, confidence. When one becomes disappointed in his service to the Supreme Lord, that disappointment must be rejected and replaced with confidence in attaining the ultimate goal, love of Godhead. The devotee should patiently follow the rules and regulations of devotional service so that the day will come when he will achieve, all of a sudden, all the perfection of devotional service. He should not lament for any loss or any reverse in his advancement in spiritual life. This patience (dhairya) is the third positive item for advancing in devotional service.
Furthermore, a pure devotee is not envious, hateful, or lazy in the discharge of devotional service. Confident of his advancement, he continually performs his prescribed devotional duties. This is called tat-tat-karma-pravartana.
The last two items are saṅga-tyāga, giving up the association of nondevotees, and sato-vṛtti, following in the footsteps of the previous ācāryas. These practices greatly help the devotee remain fixed on the path of devotional service and avoid the tendency to enjoy temporary, material things. Thus the activities of a devotee remain always pure and without any contamination of the material world.