Start with the old writings. Ones that have stood the test of time.

I know it's simpler to go on Medium and read a 1000 words article. You can do it, but always consider what's in old books more important.

- Meditations by Marcus Aurelius,

- Letters from a Stoic by Seneca,

Then you have modern books I like, but I don't know what they are worth :

- The obstacle is the way, Ryan Holiday

- Ego is the Enemy by Ryan Holiday