Complete Immediate Tasks
Finish immediate duties, so that you are able to dedicate more time and energy to whatever responsibilities the future holds. This way, the previous jobs that had to be done in the past will not be added to whatever one has to do in the future, so as to avoid making the workload heavier. When you firmly conclude the present duties, you will be able to handle future responsibilities with fresh thoughts and a sufficient reserve of energy.
Keeping Good Thoughts
Know the quality of your life is connected to the quality of your thoughts. Consequently, when your thoughts are the kind that brings benefit to you in your life and religion, then you will live a good, happy life, and the opposite brings the opposite result.
Overlooking People's Harms
Know that whatever bother the people can cause you, especially by uttering evil words, will not harm you but will harm them, unless you concern yourself about it and allow the concern to consume your thoughts.
In this case, you will be bothered (become depressed, sad and aggrieved) just as they will be bothered (by Allah for their errors); but if you do not concern yourself (about people's evil actions and statements against you), then they will not bother you in the least.
Engage in Beneficial Thoughts
In order to keep yourself busy and away from the causes of sadness and misery, then dedicate your attention and thoughts to all that carries benefit, and strive to achieve your goals. Do not engage your mind in thinking about harmful things or thoughts that are negative.
Furthermore, make good use of leisurely time so that you gather your strength to perform the important jobs that necessitate your attention.
Extracts from How to Achieve Happiness by Shaikh Abdur-Rahnam As Sa'di