The Question: what can I do?
You must
- Accept the position you are in and cooperate in as friendly a manner as you can
- Find out how to communicate your whereabouts properly, and do so consistently
- attempt to improve significantly within 30 days
- work 9 to 5
- make up for long lunches
- move your desk
- produce the written plan
- Above all else, try as hard as you can to find a new job within the 30 days
As has been pointed out, a Performance Improvement Plan is often the very last step before getting fired. Certainly this isn't the first time your boss has indicated that your performance is sub-standard. Unfortunately, the last time you hear it will almost certainly be in 30 days when you are terminated.
The steps you are required to perform are necessary to have any chance to save your job. Unfortunately, it most likely still won't work.
What do I put in that plan, besides the obvious points?
Just put in the obvious points, and indicate that you will try hard. While you can attempt to salvage your job here, your main goal should be leaving on as good terms as you can salvage. There's a big difference between leaving when you aren't a good fit for the role and leaving after you just didn't bother trying. The former case can get you good referrals, the latter case almost certainly won't.
Do I refute his false claims? We have a similar discussion scheduled for tomorrow.
It almost certainly won't matter. When it reaches the Performance Improvement Plan stage, the discussion about false claims is usually moot. You have already indicated that there is at least some merit to the overall claims - finding a point or two that isn't accurate is unlikely to matter, and will just come across as complaints from a failed worker.
Do I communicate the fact that micromanagement will not help? My boss was very hostile towards me in the meeting, pointing out that there are only two ways out of this, and that I 'know where the door is'. It is the first time he is leading a team, his last position was that of the product manager. Since he started one year ago our team has shrunk by 30%.
Again, you are on a Performance Improvement Plan path. Pointing out your boss's failings isn't going to help.
More information here: Is it illegal for a manager to admit a Performance Improvement Plan is just a formality?
(Note: If you are in a union position, you should be talking to your local union rep. Everything is different when strong union rules exist.)