While genetics will always come into play, there are a few things you can do to improve the overall appearance of your physique, and create the illusion of having a smaller waist.
1) Create a V taper
By having wider shoulders and upper back, you create the appearance of having a smaller waist! My favourite exercises for creating a wider back are definitely wide grip pull ups/pull downs.
2) Avoid over-training obliques (muscles at the sides of your abs).
While having a strong core is important, I find over-training your obliques, especially with weight – will create the appearance of a thicker waist. I like to stick to variations of abdominal crunches.
3) Most importantly – Proper Nutrition.
Consuming a healthy diet void of highly processed foods and foods that you may be allergic/intolerant to will help you lose fat overall, not to mention reduce inflammation and bloating that cause your waist to look thicker.