How to copy other artists' work to sell:
Step one: DON'T.
Don't do it. Why?
1. Because it's stealing: when you swagger-jack another person's original work, you are stealing their idea and pretending it was your original thought. (Remember plagiarism? From school? Oh hello, it's back.)
2. Because it's lying: You're telling people that you did this thing- whatever it may be- and that you did it because you thought of it. That's a lie. Because you didn't think of it. You saw it on Pinterest, Instagram, Facebook, or in a friend's house, and you copied it.
3. You'll get caught: One day, through some stroke of luck, the person who painted or created it first will see that you've built a business on the back of their idea and creativity, and there will be an embarrassing moment when you have to admit to all of your fans that you were lying. And there are legal repercussions, too.
A final note: just because you see something online that makes you think, "Oh, I could do that!" does not mean you should. I'll say it again for the people in the back: just because you see art or typography on Pinterest and you think that you can do that thing and sell it like they do does not mean you should.
Go ahead and make it on your craft day. Have a good time, and post a picture and tag the actual person who inspired it. But don't build a business on your copies. It hurts the artist responsible for the original work- literally, it hurts their feelings and their business.
So next time you see someone hustling to make her art a business and you think: "wow, I could paint what she's painting and make a killing!"... Don't. It's a terrible thing to do.