How to structure presentation to avoid getting questions that will be answered later in the presentation?
I'm constantly being asked questions that will be answered later in the slides.


You have to understand that this is a great problem to have. There is nothing worse than giving a presentation and facing a bunch of blank stares. Questions mean that 


People actually understand what you're talking about.
They care enough about your idea to actually ask.
The problem you're explaining is not trivial.
You actually have an answer to the question - later in the slides!


You mention both conference talks and lab talks. In the first case you need to be a bit more prompt (always respect the time assigned to you in a conference, you're not alone and you'll put everyone in an awkward position if you go over time): just say "this is a great question, can we wait for the next slides?" or "can we take it offline?". I have yet to have seen anyone respond to this by insisting that you answer them right now.


  But there are sooo many questions being constantly asked and it completely throws off the presentation because constant tangents are being drawn and one person's question confuses another person.


This is less a problem of structure than a problem of you not controlling the discussion. If there are many questions and people start discussing amongst themselves you need to take command of the room - say, "it's great that we're having this discussion, but I'd really like to move forward!", or something to that effect.

I believe that neither of your approaches (if I understand them correctly) is as effective as it can be. In conference presentations you need to focus on one big idea and explain it well - the objective of the presentation is to get people to read (and cite) your amazing new paper. Avoid giving broad overviews, and getting into every little detail. The audience needs to know why they should spend time reading your paper, and that's it.

In lab presentations make sure that the group knows what the big plan for today is. If there is a constructive discussion that's great. Tell them in the beginning the big points and then try to cover everything else. Give references to stuff you didn't cover so that the group knows where to look for things that weren't covered in the presentation.

Good luck!