It’s important to treat people of different religions with respect and compassion–just as you’d like them to treat you.
Even if you think your religion/faith is correct… how does that give you reason to treat people of other faiths condescendingly or (just) poorly?
The best da’wah (calling others to your faith) that you can make is treating people with respect and love, after all.
We are all one human race. Whether you believe in Allah, Krishna, Jesus, the Buddha, or whoever., each of those beings that we worship would want us to be compassionate towards each other. (what I mean by that is: e.g., I personally don’t believe in Jesus Christ as God. But for those people who do, we would all agree that Christ (whether the Islamic conception of him as prophet or the Christian conception of him as Lord) would want us to be kind to one another regarding our beliefs).
In other words, we all agree that all of the different gods/conceptions of god that we as humans worship are good, benevolent, and kind. None of them would want any of us to be mean to anyone else (especially on the basis of religion, it could be argued).
Personally, how I approach the topic of dealing with people of other faiths (other than Islam) is that I like to explain to them what Islam is, and just why I believe it is the final, true guidance from God (this description of Islam being one of the most core definitions of the faith that one can say). But, I also make sure to let the people know (at the end of my da’wah–calling to God) the Islamic idea of “la ikrahaa fil deen–there is no compulsion when it comes to religion” (Qur’an–chapter 2). The idea that no one can be forced to believe in anything is fundamental, in Islam (so much so that “forcing” others to “accept” Islam is absurd… partly because the new converts’ faith will not be acceptable, to Allah (because it is not true faith–they were forced).
Anyway, the point is: all anyone (of any faith) can do is lovingly try to get others to embrace their faith. But if the others don’t (I know I, for example, certainly will never accept any other religion besides Islam…), then the chapter found in the Qur’an that says “…O you who reject faith! I do not worship what you worship, nor do you worship what I worship. And I will not worship that which ye have been wont to worship, Nor will ye worship that which I worship. To you be your Way, and to me mine*” applies.
Peace be with you…~
*Qur’an. 109:1-6. Yusuf Ali translation.