All good advice.
Also, I find that some vowel sounds need to be exaggerated in order to sound like the word it's actually supposed to be. Like instead of singing "follow", sing "FAR~LOW". It sounds stupid as you do it, but when you listen to it, it sounds like you're singing "follow".
I tend to enunciate my words but I've developed a fast mouth over the years so it sounds relaxed and not like elocution lessons. Enunciation however, isn't that important in some songs. But I'd say learn to stretch vowels and get around lots of words and syllables, fast and in tune. It soon becomes normal so even if you're forcing rhymes and squeezing in syllables, you can make it sound relaxed and natural. Or tense and natural. Or angry and natural. Or sarcastic and natural. Or miserable and natural. You get the idea.