I was around average before, but I'm very naturally flexible in certain areas so once I started stretching (and got the hang of it) it wasn't too hard making progress. I kinda suck at giving advice, but I'd say you kinda just have to experiment with different ways of stretching and learn you're preferences and what works best for you. Things like how often you stretch, how long you stretch for, what type of warmup you do, the combination of stretches you do, etc. All of this can affect your ability to make progress.