Hi,
with questions like this, you are getting into trouble, lol.
I remember asking the same kind of question in the past. I've never gotten a clear answer, because this can get very complicated, as you can see from raindoctor's answer.
It depends on what you want to know and why. If you just need some tips to improve your spoken English then you don't need to know any complicated stuff.
What I can tell you, as a non-native speaker, is that every feature of a spoken language can vary. Take the dark-L for example: ok, it's dark, but how dark? It's impossible to tell how dark an L should be, because it varies from accent to accent, depending on what comes before or after the L, and sometimes it might not even be an L anymore in some accents.
Spoken English is a mess.
This is how I think I'd currently say the L, for example:
#1 COOL = Very dark L, tip of my tongue doesn't touch the roof of my mouth
#2 LINE = Normal initial L, which is dark anyway, but less dark than #1
#3 COOL INDIAN = Very dark L, but my tongue touches the roof
#4 CALIFORNIA = It varies depending on how fast I try to say it. The slower, the darker.
I don't think it's worth finding a pattern to follow though. I would expect countless personal and dialectal variations.