Not Giving the Rights of the People

The Holy Prophet (s.a.w.s.) said:
"I have been commanded by Allah to warn my people and say, 'Do not go from one mosque to another while someones rights are upon you. If such a person stands up for prayers in that condition, I send my curses upon him till he restores the rights to its owner." (Iddatud-Dai page 236)

Eighth Tradition

The Holy Prophet (s.a.w.s.) said,
"There is an angel of Allah who raises the call every night from 'Baitul Muqaddas': "Whoever partakes of the prohibited things, Allah does not accept any of his deeds be they obligatory or recommended."
(Iddatud-Dai)

Good Deeds are Accepted Only if Accompanied by Piety.
(Abstinence From the Prohibited Things)

Ninth Tradition

"Even if you stand for prayers like a tent peg planted on the ground and keep fasting till you resemble a dried stick and stoop like a bow, Allah will not accept any of your deeds till you have the piety to guard against the evil deeds."
(Iddatud-Dai)

Sin is a Barrier to the Acceptance of Invocation (Dua)

Tenth Tradition

Hazrat Musa (a.s.) passed by a person from his followers who was in prostration. After completing his chore Musa (a.s.) returned to find him still in prostration. He said, "If I had the vigor to grant your wish I would surely have granted it." Allah disclosed to Musa (a.s.) that, "Even if this man prostrates for Me till his head gets detached from his neck, I will not accept his deeds, till he abstains from that which I dislike and does that which pleases Me. Otherwise sin hinders the supplications from acceptance."
(pg. 125 ibid)

Refraining From Sins is Genuine Worship

Eleventh Tradition

"Abstaining from sins is the basis of religion. Hence, refrain from sins in order to become the most pious worshipper. Adorn yourself with piety. Do not perform a single good deed without piety. Surely that deed is most acceptable by Allah which is accompanied by piety, even though it may be trifle. As Allah says, "Allah accepts the good deeds only from the pious people."
(Iddatud-Dai)

Hence if you succeed in remaining aloof from sins, then even if your good deeds are paltry, they would be accepted by the Lord. And when the Lord of the Worlds accepts a deed it cannot be termed as trifle or paltry.

Avoidance of Sins is a Must:

Considering the tradition quoted above one is compelled to conclude that it is necessary to dread sinful acts and to be ever cautious of the vices. Only then are the good actions of any consequences. The good deeds must also be performed in such a manner that we strive to emulate as closely as possible the examples set by the high ideals of our Ahlul Bayt (a.s.). It should not be that good actions are rendered null and void due to sins. It is necessary to be cautious of such an impending loss and disaster for which we ourselves would be responsible.

Good Actions Could Be Blown Away Like Dust

Sulaiman bin Khalid says; " I asked Imam Ja'far as-Sadiq (a.s.) regarding the Quranic verse

(And We will proceed to what they have done of deeds, so We shall render them as scattered floating dust.
(Surah Furqan 25:23)

He said,
"By Allah, even if their deeds are as white as Egyptian cotton, but if they find sin and lewdness they do not abstain from it."
(Iddatud-Dai)