Here are some suggestions I added on older threads on this subject:

There are some classic exercises for warming up your mouth and using vowels and consonants while you sing exercises - try singing scales up and down on the sounds "mada meena mada meena mada meena mah" and "kagle ogle agle ogle ay". Lift the soft palate and relax your jaw and neck muscles. Open your mouth in a relaxed way, don't block the sound from coming out.

Using that exercise, work on getting clear vowels and consonants. Relax. Sing/speak on the vowels, to keep your sound open. Don't hammer "k" sounds, don't let all the air leak out on "h" sounds, don't hiss on the "s" don't hang on to nasal "r", "m" or "n" sounds. Don't break words and phrases in the middle (a bad habit in pop singing right now). Have enough breath to carry you through to the end of a word or phrases (this is where learning breath support comes in).