You don't hold in a tense way or try with effort to get rid of thinking. The more you relax within attention the more you hold. It is more about letting thoughts go in order to stay on the object of focus. If the object is a stone then the thoughts are like a fast running stream - you don't watch the fast running stream you watch the stone - the fast running stream just goes by itself.
So relax to build attention. The more you relax into things with attention the better your meditation gets. But don't get stressed about relaxing.
The Blessed One said:
"What is the All? Simply the eye & forms, ear & sounds, nose & aromas, tongue & flavors, body & tactile sensations, intellect & ideas. This, monks, is called the All. Anyone who would say, 'Repudiating this All, I will describe another,' if questioned on what exactly might be the grounds for his statement, would be unable to explain, and furthermore, would be put to grief. Why? Because it lies beyond range." Sabba Sutta.