How are we supposed to address Muslim sinners to explain and convince them that it's not sufficient to pronounce the Shahadah, pray 5 times a day, and fast the month of Ramadan to enter Paradise? Nowadays many Muslims think this is enough for them - and they don't do any more good deeds, instead they commit major as well as minor sins. So, please tell me ways to convince them that they have to work hard to gain Allah's Pleasure and Paradise.

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

All the pious predecessors are agreed that Iman is a belief in the heart, words to be uttered, and some actions to be performed. These three elements are complementary and none has any effect without the others.
So, if the person believes in his heart, says the Shahadah with his tongue and performs prayers and fasting, he is counted among the believers whose fate, in the end, is Paradise, by Allah's Will, even if some of these people enter Hell for a period, depending on the extent of their sins.
So, nobody should or can say, "I am from the dwellers of Paradise", no matter how good he is or how many good deeds he performs except those whom the Sharia texts prove they are from the dwellers of Paradise. Therefore, those who commit sins and continue doing so and at the end say: "Allah is Most Merciful Most benevolent" although this expression is true but are mistaken, as this argument is pure ignorance and Satan insinuations.
The way to call people to the right Aqeedah (creed) and to perform good deeds is with patience and by teaching the creed of Salaf (the righteous ancestors) and reminding people of Allah and The Last Day and all the benefits and advantages they will receive by following the right Aqeedah.
Allah knows best.