Think clearly.
Reason well.

"You can't trust his climate research — he drives an SUV."

Attacking the person making the argument rather than the argument itself. A scientist's lifestyle doesn't invalidate their peer-reviewed research. The most common fallacy in online discourse. Counter: "That may be true about them personally, but what about the evidence they presented?"

"You want to reform policing? So you want criminals running free?"

Distorting someone's position into an extreme version and then attacking that distortion. Nobody argued for "no police" — they argued for reform. Counter: "That's not what I said. Let me clarify my actual position."

"A Nobel Prize winner in physics says this economic policy is wrong."

Citing an expert outside their area of expertise. A physics Nobel laureate has no special insight into economics. Legitimate appeal to authority requires the expert to be speaking within their field AND there to be consensus among experts in that field.

"You're either with us or against us."

Presenting only two options when more exist. Most complex issues have a spectrum of positions. Counter: identify the missing options. "Actually, I support parts of both positions, and here's a third option you haven't considered."

"I've already invested $50,000 in this startup — I can't quit now."

Continuing a course of action because of past investment (time, money, effort) rather than future prospects. Past costs are gone regardless. The rational question is: "Knowing what I know now, would I start this today?" If no, cut your losses.