How do I write lyrics that sound big and intelligible and not mumbly?

I've been having problems with writing and recording. My friend says my songs sound mixed and mastered good but my words are sometimes big and sometimes small and some words are hard to understand. I want to know what letters or words can I use to make my lyrics sound big. Like I need my letters to sound big. Like when I look in the corner of my eye to the left, I see small letters when I just want to just see and have my letters be big like Drake or any artist for that matter.