Place the scallops flat-side down in the hot pan. Don't overcrowd the pan, or the pan won't stay hot enough to give the scallops a good sear. If you have a lot of scallops, it's better to work in batches.
Another important tip: Once you've placed the scallops in the pan, don't touch them! If you give in to the temptation to move the scallops around the pan, all you'll be doing is preventing them from forming the nice brown crust that you want. Be strong!