My favorite gear advice--three of them:

When selecting new gear, get the lightest item you can find that meets your needs. The last part is the most important!

At some point, the "law of diminishing returns" applies to lightweight backpacking. The dollars spent per ounce saved sooner or later become prohibitive. At that point, it's time to look for other ways to save weight.

With new gear, or when taking less gear: Stay close to home, or at least to your car, the first time or two out with new gear or a different gear configuration. Four days from the trailhead on a week's backpack is not the time to find out that you left one layer too many at home!