It doesn't always have to be an hour-long meditation session or exercises that can make someone mentally strong.
Sometimes these essential habits can equip your mind and not let negative thoughts enter at any time.

Make Your Bed.

-Say Nice Things to Yourself Daily.

-Write Down Something Great About Each Day.

-Write Down the Positive Aspects of Every Challenge.

-Practice Mindful Happiness While Commuting.

-Practice Being Your Own Best Friend Daily.

-Practice Saying "o" "without Explanation.

-Practice Saying "o" "without Explanation

-Do a Hobby or Activity Daily Which Brings You Joy

-Set a Goal to Practice More Gratitude and Less Complaining

-Put up at Least Three Inspirational Quotes to Read Daily

-Visualize Your Goals for 10 Minutes Daily