Yes it is totally fine to give yourself verbal instructions. SSILD is a very forgiving technique and that's what sets it apart from others. You seem to be applying too much effort on "focusing" though. Just cycle through the senses regardless of what you actually see, hear and feel. It's the "gestures" that are more important. Even just telling yourself "I'm now focusing on hearing..." should be sufficient. Having said that, after you quickly go through a few cycles it actually becomes a lot easier for you to actually focus, and you may even experience various sensations. Do keep in mind -- the sensations are nice, but they are not mandatory.