It's pretty easy, really. All you have to do is something that looks like it could be criminal but is not. As long as it gives rise to probable cause, you're a target for forfeiture.
Imagine this: You're moving across the country. You've cleared the money out of your local bank and you're taking it with you, with plans to use it for a down payment on a new house. You've got $63,000 packaged up in a box, in your trunk for safekeeping.
Risky? Yes. Illegal? No.
Anyway, police think they see you breaking the law. You weren't, though, so you stop and fully cooperate with the police, who decide there's no reason to write you a ticket. But they want to ask a few more questions: Do you have any drugs? Weapons? Bundles of cash? You just want to get back on the road instead of explaining why you've got the cash, so you just tell them no.
But they want to look in your trunk. They do, and they discover the cash.
So they take it. They ask if it's drug money. You tell them it's not. You've got your whole life in your car, so you let them look at your bank records, pay stubs, etc., to prove it.
They don't believe you. They bring out the drug dog, and it barks at your car. They search, but they find zero drugs. They find zero drug paraphernalia. But they do find a magazine with articles about marijuana, so they still think it's all a little fishy.
So they take all your money.
What do you do? You are now forced to basically sue the police to get the money back. And the burden is on you to prove that it isn't from some crime. But the judge doesn't like that you lied about the money. (Never mind that you don't have to tell the police when you're carrying a lot of money) Or that the drug dog said there were drugs in your car. (Never mind that there were no drugs.) Or that your testimony was self-serving. (Never mind that that's the whole point of the hearing.)
So the judge rules against you and says the police get to keep your money. That's obviously insane, so you appeal to the Eighth Circuit. They tell you to pound salt. The police keep your money and buy some nice new toys.
That's basically what happened to Mark Brewer: U.S. v. Brewer, 781 F.3d 949 (2015). Never charged with any crime. Never convicted of a crime. Out $63,000.
So the answer to your question is that if you don't want to be on the wrong end of civil forfeiture, you must refrain from possessing anything that a police officer could reasonably believe was related to a crime. This is unfortunately impossible, so the real answer is that you have to write your lawmakers and tell them to end civil forfeiture.