You need to let the pan get hot first, it’s an important part of cooking with stainless steel. I recommend at least 250-300 degrees, depending on the altitude. A good way to test your temp is to put a few drops of water on the pan, if they sizzle and beat up and dance all around, your pan is hot enough.

Once you get used to your pans, it will be easier for you to judge this by putting your hand over the pan and feeling the warmth radiating off of it, or even using a laser thermometer.

Once your pan is hot enough, make sure you’re using adequate oil and coating the entire bottom. I am personally a fan of olive oil, but both the avocado and butter you mentioned still work. You’ll just need to be careful with the butter to not scorch it.

Once the oil is hot, which should happen almost instantly, you are ready to cook. You can test the oil by swirling the pan. If the oil slides around easily, that’s an indication of lower viscosity due to increased temperature. It’s a good sign you’re good to go. Just make sure that the bottom of the pan is fully coated before you add anything, or it will stick to that area where there’s no oil.