I try to think of pacing as how fast time goes for a charachter and that I need to control how quickly or slowly it passes or flows. To me it depends on how important a particular moment is to the charachter. If it is a moment that is going to have a compounding effect on that charachter, say for example the moment, the second it can take for you to realise a person is dead, I would think it would need more than a sentence. It might only be a second, but that moment and the emotion of the MC could be explored. But if he or she notices a cat, but that cat isn't really that important but just a part of the scene setting, we probably don't need to spend a paragraph describing it.
Pacing I think is gained by varying word, setence, and paragraph length.
If you have a charachter running through the woods, or streets, you might use short sentences, maybe to keep pace with their breating or something. If you have a charachter going for a slow boat ride, you sentences might be long, flowing, to give an effect to the scenery.
If you have a gape between scenes where nothing of interest happens, you don't want to bore the reader with the charachter dressing, or making dinner, unless it is part of the plot and needed.
Two many or said tags placed when not needed will slow down pace also, as will wordy sentences that have no purpose, and long flashbacks or backstory unless handled very carefully. Once you take a reader back in time, it can have the affect of making the reader become bored with hearing about something in the past. If not done properly you will rip the reader out of the moment, make them wish they could get back to the future, and in turn slow the pace down.
Hope some of this helps.