What's the best way to test form field optimization?

As a Shopify store owner, I've been pulling my hair out trying to understand why potential customers abandon their checkout process. My conversion rates are decent, but I know there's room for improvement. Every time I look at my analytics, I see drop-offs happening right at the form submission stage. Are people getting frustrated? Is the form too long? Too complicated? I've tried making minor tweaks, but without a systematic approach, I'm basically throwing darts in the dark. I need a structured method to test and optimize my form fields that doesn't require complex coding or expensive consultants. My goal is to reduce friction, make the customer experience smoother, and ultimately increase my store's conversion rate. But how do I do this methodically and scientifically, without guessing or wasting precious time and ad budget?