Quoting few verses for Surah Abasa (Chapter 80)
80:5
أَمَّا مَنِ ٱسْتَغْنَىٰ
As for he who thinks himself without need,
80:6
فَأَنتَ لَهُۥ تَصَدَّىٰ
To him you give attention.
80:7
وَمَا عَلَيْكَ أَلَّا يَزَّكَّىٰ
And not upon you [is any blame] if he will not be purified.
80:8
وَأَمَّا مَن جَآءَكَ يَسْعَىٰ
But as for he who came to you striving [for knowledge]
80:9
وَهُوَ يَخْشَىٰ
While he fears [Allah],
80:10
فَأَنتَ عَنْهُ تَلَهَّىٰ
From him you are distracted.
I hope everyone knows why these verses were revealed - if not I can explain.
The main lesson of these verses is to focus on the people who are interested to gain guidance and not to waste our time who are transgressors and their purpose is clearly to misguide others and spread corruption in the society.
This is what I generally put in practice regarding non-Muslims.
Anyone who seems to be interested in Islam, I try to engage in a dialogue in a respectful way. Normally I begin by giving them a copy of Quran to read and for the most part that's all what someone needs to accept Islam. If they have any questions, I try to answer their questions without engaging into arguments and making fun of their belief systems. For those who are not interested in Islam and actually engage in making fun of Islam and Muslims, I don't engage with them.
Another important aspect is to preach in your own community, in your own neighborhood and work place. For that it is also important to put Islam into practice to an extent that even non-Muslims at my work or neighborhood could say that this guy holds good moral values, in other words try to preach Islam with our actions rather than lengthy arguments and discussions. Sometimes action speaks louder than words. Prophet (peace be upon him) lived with his people for 40 years and only then he (peace be upon him) was given the Prophethood. By that time, he was already know to be the one with best manners and whatever he would say will carry weight. His first Dawah was also to his immediate family members and his own tribes men.
Preaching Islam on internet and forum is waste of time, that's just my opinion. No one knows the other person and usually the whole exchange comes down to personal egos. I prefer to have face to face interactions to have a more meaningful outcome.
Lastly Dawah is not Fard on everyone. It is fard al-Kifaya means it is not obligatory for every individual Muslim; when some Muslims fulfill it, others become exempt from it. If nobody fulfills it, then the whole community becomes responsible for it and everybody is regarded to have committed a sin; like performing the janazah prayer when a Muslim dies.
Those who have very little knowledge about Islam ( like myself), should work on learning Islam and try to protect themselves first. They can donate money to Professional Dawah organizations such as
iERA & let the professionals do their job. We can still get reward by sponsoring them financially.
And Allah knows the best!
Ma'aSalaam