Is there a difference in meaning between the following two sentences?
Which one is more appropriate when announcing to your family that lunch is ready?
用意が出来ました means something have just become ready, whereas 用意が出来ています means something is (already) ready. Use the former to someone who has been waiting for the lunch, and use the latter to someone who have just returned home.
See these questions if you're not sure why 出来ています means such a thing:
( There's a great answer already. So I'd add ... )
The first time, a person says: 昼食の用意が出来ました。
5 minutes later, he/she may say this: 昼食の用意が出来ています。-- ( to mean that [it has been ready] -- so it can be sarcastic, nagging, etc.)
When is Vている the continuation of action and when is it the continuation of state?
( "Last night, when I asked my wife to send an email to me, she said もう送っている ... " )
When she said, もう送っている (it's been sent already) -- it can be (or can have small elements of being) sarcastic, nagging, etc.
For 「昨日 寝てない」 there are a few different possible interpretations.
present perfect 「昨日から 寝てない」
general condition, habit 「最近 よく寝てない」
(past perfect?) or Experience
3a. Preparation, e.g. for a test. --------------- See: Meaning of 寝てない