From my experience these are things that helped me improve:
- Race selection. It needs to suit your strengths and needs to be a fast one. The difference between slower races like Lanzarote and the fastest like Florida or Barcelona are huge.
- Consistency. If you are consistent with training over multiple years you'll get better
- Frequency. If you train more often you will improve. Going from 2/2/2 to 3/3/3/ or 4/4/4
- Volume. With more volume you will improve. Tracking how you spend your time might help you optimise and finding more time.
- Manage intensity. Have high intensity but not too much. Too much will get you injured or sick. Consistency is the most important thing.
- Get a coach if you don't have one.
- Better equipment can get you a lot of speed on the bike
- Better pacing at the race (don't swim or bike too hard)
- Better race nutrition (a little more liquids, a lot more carbs. 90g of carbs per hour or more)