Associate with intelligent people.
Ignorant people will harm you more than they will benefit you, even if they’re your friends.
Omar Khayyam says in a poem:
اشرب نقيع السم من عاقل
واسكب على الأرض دواء الجهول
“Drink the Infusion of a Sane person’s Poison,
and Pour on the Ground the Ignorant’s Remedy!!”
