The trick is to hold off on taking out your weapon until you’re sure you have a clean shot at the opponent and you’re ready to execute.
This may seem self-explanatory but it’s important to keep your builds out the entire time when you’re engaged in a build fight. This will allow you to build with greater fluidity and not be interrupted by having to switch back and forth between your loadout and your build menu. The trick is to hold off on taking out your weapon until you’re sure you have a clean shot at the opponent and you’re ready to execute. If you learn to demonstrate composure and incorporate this tiny change into your game it should allow you to build and edit with greater speed and accuracy.