I have ALREADY done it. (Between Auxiliar and Main verb)...Yes, this is the most common position for 'already'. As Claire says, you could also put it at the end of the sentence: "I've done it already."
I STILL haven't made a decision. (After the subject) .....'still' is only before the auxiliary 'have' because you have (rightly) contracted 'have' and 'not' (making 'haven't'). The position of adverbs that usually come between the auxiliary and the main verb is often changed in the negative, because of using contractions.
If you didn't use a contraction, the sentence would be "I have STILL not made a decision" (but this sounds a bit formal, so it's best to stick to 'haven't' and put STILL before it). There are other ways of doing this also, but I don't want to give you too much information and confuse you.
I've STILL got another three files to finish.
I STILL haven't finished the files.
I have JUST spoken to her (Between Auxiliar and Main Verb)....correct. We would usually contract it to "I've JUST spoken to her" in speaking, and also in informal writing.
But I was wondering if it is correct to say:
I ALREADY have done it. .....incorrect.
I haven't STILL made a decision....incorrect, because 'still' has to come before the negative of the verb (go (positive), not go (negative)....laugh (positive), not laugh (negative).....made (positive, past), not made (negative, past)). 'Still' shouldn't come between 'not' and 'made'.
I JUST have spoken to her.....incorrect