How to Pray
Just recite as many times as your time allows unless instructed by master.
Usually prayers are done before wearing the amulet, after taking off the amulet, or before sleep.
You may of course chant the katha while you are doing other things, such as driving or walking.
However, attention should be prioritize on the thing you are doing, to avoid unfortunate event.
If possible, pray after you practise meditation, to assist your concentration (samadhi) and awareness while reciting katha.
Reciting with samadhi and awareness will bring much difference compared to plain mouth or heart recitals.
Know what and why are you reciting.
Mechanical recitals, especially after you have memorized and have been reciting the kathas for some time, does not bring much effect.
Respect the entity of your amulet and its maker.
Appreciate it, its existence, and your luck of owning it.