What's the best way to keep my 16' flatbottom from drifting in the wind with a bow and stern ancher. Do I point the bow into the wind, or ancher sidways to the wind?

That would depend on the wind.  In a 16, flat bottom, 20-25mph winds will be about as strong as you'll want to anchor in sideways.  

Have you looked at drift anchors?  I'm not sure if you are really looking to lock down on a spot or just be able to fish in the wind.  If not looking to lock down, I HIGHLY suggest grabbing a drift anchor.

DO NOT anchor "Beam to" in stiff winds OR where boat traffic might create heavy wakes! One good one over the side may well start you on the way to Davy Jones Locker.

If you must anchor, in all but the calmest waters, do so from the bow, which will cut the waves better than the beam or stern. If possible, attach a small buoy to the anchor line and provide for an instantaneous release of the anchor at the approach of a dangerous wave/wake.

Two better approaches:

Use a drift sock, preferably at the bow, to slow your drift. If you have a splashwell and a WORKING bilge pump, then attaching it at the stern may be OK. NOTE: If the boat rides low at the stern...fuggidaboutit!! Make sure the drift sock has a quick dump strap so that you can collapse it if danger threatens. You won't have to try to haul in a loaded sock, just pull the strap and she empties.

OR: If possible, use "brush clips" (NOT knots, unless they release with one pull,) to secure the boat to available trees, bushes, etc.

Good luck and above all, be safe.

FlyRod

Good points fleye rahd.  I tend to answer based on myself sometimes.  My boat on my pond (elec only) and forget that many live on lakes that have real traffic and wide open areas etc.

I recently finished up a boating safety course, and one point that was made about anchoring is that you should anchor from the bow only.  Anchoring from the stern (rear) of the boat can be dangerous, for the reasons that F Rod stated above.  It is much easier to get swamped when you anchor from the stern.