Install Google Analytics 4 the moment you decide to track user behavior—ideally before you run your first ad, publish a redesign, or start creating content at scale. Waiting until after a campaign or site migration means you lose the baseline data needed to measure impact. You can't retroactively fill gaps in GA4; every day without tracking is a day you can't compare against later. Prioritize conversion setup in the first week. Define key events like form submissions, purchases, phone clicks, or file downloads immediately, even if traffic is low. GA4 learns audience patterns and attribution over time, and events configured late won't have historical context. If you launch a campaign in March but only mark conversions in May, the earlier period may not contain the event definitions needed for the later comparison. If you're migrating from Universal Analytics or starting fresh, run GA4 in parallel for at least thirty days before making decisions. This overlap lets you validate data accuracy, spot discrepancies in session counting or event triggers, and train your team on the new interface without pressure. Don't wait for perfect traffic volume. A new site with fifty visits per week still benefits from event tracking and user-path data; you'll see patterns emerge as volume grows. Configure custom dimensions for product categories, lead sources, or client types early—adding them later means months of untagged sessions. Watch out for default data retention settings. GA4's standard retention is two months for user-level and event-level exploration reports unless you extend it to fourteen months in the admin panel. Set this before you collect data, or older cohorts disappear from custom reports. Also enable Google Signals if you want demographics and cross-device insights, but remember it only applies going forward. Timing matters because GA4 builds predictive audiences and attribution models from accumulated history, and you can't manufacture that after the fact.