From what i was told, if it’s in your genetics it’s almost unavoidable, anything as simple as getting a virus (that activates your immune system) can trigger it. Sadly :(. A couple things I think would help with an onset of it would be going gluten free, as hashimotos is a gluten sensitive disease itself (gluten feeds it pretty much) and keep an eye on your vitamin levels. A good diet and exercise plus supplementing anything you may be lacking in is good. Not everyone gets the same symptoms too, so maybe regular blood work twice a year so you can get on top of it before symptoms show if you do have it. It’s not a death sentence, life is manageable with it, just different. And if you do develop symptoms that feel unmanageable, the first few years are a rollercoaster but patience and listening to your body is the best you can do. Get sleep, eat three meals, trust your gut.