Mantras themselves have great power because they are holy words, but if we just say them without any feeling we will quickly just find ourselves bored. When we say these words, we should be trying to become the mantra. This can mean one of two things. If we are saying a mantra that represents what we want, we are attempting to manifest this into reality and we should feel positive while saying it because it is already true. If we are saying a holy mantra such as Sanskrit or one for enlightenment, we should be trying to become a vibrational match to the mantra, and ascend into its power. These are good to be said during meditation when your mind is clear and your mind will not fight against what you are saying. You should also give the effects some time and not wait on them, because feeling anxious about the results can negate the benefits of the mantras.