One thing that really helps elevate your garments is measuring. And often it is not necessary to use a tape, but instead to use what I call “the rule of symmetry”. Just verify that two sides/collar points/buttonholes/whatevers are the exact same size before you proceed to the next step.
I am especially picky about collar points because they are right near your face and are a real focal point for a shirt. Match ’em up, and if you need to make an adjustment of course you need to do so before adding top-stitching. I usually don’t bother with getting a seam gauge or a tape; all I really care about is that they are the same length. Not that many people are going to have the pattern piece in their pocket to check my accuracy against the pattern length specified. 😉
Happy sewing!
Maris