I've read a lot in "Answers In Genesis"'s stuff about how the foundation is so crucial; people think there is no reason to exist, that they are just an accident, at times. They not only need to see a loving Creator, they need to see that He created them for a purpose. That we aren't just a 'bunch of pond scum."
People try to mock the Creation story, but they really don't understand that the Bible really isn't contradictory (AiG, I believe, has a good explanation of how Gen. 2 is an explanation of how Gen. 1 occurred, with mroe detail, for isntance), and that the things others try to spout just aren't true. (The Bible says where Cain got his wife right in Gen. 5:4, that there were other siblings. We don't know how many were born before Cain slew Abel.) Many baby animals could have fit on Noah's Ark. And, so on.
Also, many times, the bad things of this world are emphasized. This, too, can be explained easily by going back to Creation. The world was made perfect. it is only imperfect because sin was brought into it. God didn't want us to be mindless robots who are forced to worship HIm. God wants us to choose to worship Him.
Also, and I'm sure you know this from talking to others, that worldview often has very poor home lives in it. So, you have to start from scratch with some; "Perfection is the way the world is supposed to be; God is very sad that people have chosen to do evil/walk out on you/whatever, but God, in His mercy, doens't destroy people right away. He keeps lovingly calling them to repent and turn to Him."
So, in sum, make sure you understand the foundation, and the worldview others are coming from.
Edit to agree with 4EvrHis, that's the real problem, it's so hard for some to see it's not a religion, it's a relationship, that they need Him to forgive *them,* It's easy for someone to think, "Yeah, those people who do really bad stuff need forgiveness." But, we all need forgiveness, because any amount of sin causes us to fall short of His perfect glory. We need changed on the inside.
And, I better stop now, or, this will develop into a sermon. :-)
John 3:16 (KJV) For God so loved the world, that He gave His only begotten Son, that whosoever believeth in Him shall not perish, but have everlasting life.