Decide if you're more a hiker, or more of a camper. If you're inclined more towards hiking, then trip planning starts with thinking about what you really need in "camp" if you do little there other than eat and sleep. It's potentially a "virtuous circle" (opposite of a vicious circle): less stuff for camping means a lighter pack, which in turn makes the longer amount of time spent hiking more enjoyable, less painful, so you're not as inclined to hang out for long periods in camp or taking breaks.

Other "style" shifts that can impact pack weight are deciding which and how many meals to cook (if any), how often you really need to change clothing (if at all) on the trail, and potentially doing more things half inside a sleeping bag in camp to reduce the amount of warm clothing needed.

Another "virtuous circle" aspect is when pack weight gets low enough, then it takes less time to do an equivalent length trip, which in turn means less food carried and thus an even lighter pack. Water is similar, in that with a lighter pack you can potentially make it to a next water source in the same day and thus carry less water on average (all within reasonable safety constraints).

Trip planning definitely can reduce pack weight by just mechanically analyzing gear and clothing carried, but to get real wins I think a person should also factor in on-trail (and in-camp) "style" issues.