The most useful habit in sight-reading is reading slightly ahead of where your hands are playing. Beginners read the note they're about to play; fluent readers have already moved on to the next one. That little gap between eyes and hands is what makes it possible to keep going without freezing.
Here's how to build it. Start very slowly. As you play the first note of a beat, deliberately let your eyes drift forward to the next beat. Your hands play what your eyes already left behind. It feels uncomfortable at first — like your eyes and hands are arguing — but that discomfort is the skill forming.
A classic drill: cover each beat with a finger or a slip of paper right after your hands reach it, forcing your eyes to live in the future. Another: pick an easy exercise and try to always be able to say the next note out loud before you play the current one.
Practice it slowly until looking ahead feels normal, then raise the tempo. Once it clicks, hesitation and those panicked full stops mostly disappear — because by the time your hands arrive somewhere, your eyes have already scouted the road.
Generate an exercise → and try reading one beat ahead the whole way through.