The chief entry way is our senses. Thus, it is necessary to have a sentry who observes what the senses are doing at all times:
eyes
ears
nose
taste
touch
thought and emotion
Then, every night, review what they sentry saw. Often, one does not realize in the moment of observation what was observed, But later, when reviewing, new information becomes available. Thus, meditation is necessary.
“Nothing is easier than self-deceit. For what each man wishes, that he also believes.” —Demosthenes
"Do not worry; cultivate the habit of being happy." —Samael Aun Weor