Singing advice will depend on the type of music you are singing.

Enunciate your vowels (Classical singing)

Tall vowels (a certain type of church music)

Singing warmups: sing up and down the first five notes of a major scale (me ee moh oh mi i moo oo oh) (Sorry no IPA)

Sing naw aw aw aw aw on scale notes 5, 4, 3, 2, 1 (so fa mi re do) going up the scale.