Journalling your experiences, thoughts and reflections can help with lots of things, including processing emotions consolidating memories and forming supportive habits.

Some people love the process and ritual of writing on paper, others prefer to capture their reflections verbally, either recorded or through a dictation software, others prefer to speak out loud to trusted other such as a partner.

Whatever you prefer, there are some prompts below, to get you started. These are taken from Rangan Chatterjee and Sahil Bloom respectively (both of their websites are linked, if you want to find out more about them). 

These three questions answered every morning and evening form the basis of his Three Question Journal - though he emphasises that you can also use a plain notebook or other way to record your answers.

What do you appreciate about your life?

What is the most important thing you have to do today?

What quality do you want to show the world today (e.g. patience, compassion, courage)?

What went well today?

What could I have done differently?

What did I do for someone else today?

Morning mood journalling:
AM: On waking:

Rate or name your mood (e.g. great/good/neutral/bad). 
Then answer two questions:

Why do I feel this way?

What is driving these feelings?

PM: Each evening, write down:

One win from the day - something that went well, however small

One point of tension, anxiety or stress - something that felt hard, confusing or draining

One point of gratitude - something you feel thankful for today

There are many more ideas around journalling, and I would love to hear what works for you.