One of the simplest ways to transform your garments from feeling homemade to looking professionally-made is by using French seams.
Instead of a simple side seam that most patterns use, French seams have you enclose the fabric's raw edges within the seam allowance.
This gives your garments a clean finish that works great for any piece, but especially well for business casual or formal wear.
This tutorial will show you how to sew French seams on a Riviera Shirt. However, you can use this for any pattern you have.