Tips, Tricks, & Methods
The construction plans lay out the recommended methods and a few tricks in good detail. In the decades since these methods were proven out, there have been a few improvements, variations, and different methods that have shown or demonstrated promise.
Some of the following I have adopted from other builders, and I have given credit where I know the originator (let me know if you notice anything missing or in error here).
I have been reading mailing list archives, forums, other builder's sites, and e-mail lists for years. Most of what I have here is adopted from what I learned on those sites and discussions. This list is not exhaustive of every tip or method out there, just what has been salient to me.
Some of this I have developed from plans or other's methods and changed for my own purposes. 
What works for me and with the exact materials I am using may not work exactly the same for you and the exact materials you are using. But hopefully some of the information here will help you build easier, faster, and lighter! Well, pick two...
Hard-shelling is, in a nutshell (sorry), a modification of the layup process onto foam. In the normal, plans method, a micro slurry is applied to the foam and then immediately laying up of the glass is done on top, such that it all cures together. 
In hard-shelling, you apply a slurry (or even a thicker micro mix, to save weight), then let it cure before doing the layups on top. Thus, creating a hard-shell of micro in the surface of the foam before doing the layup.

Being able to separate the microing of the foam and the actual layup adds a lot of flexibility during construction, as you can separate the processes into two different sessions.
There is a possible advantage of reduced weight, using a 'thicker' micro mix without fear of disrupting or contaminating the layups above.
The contour of the foam can be corrected as well, if needed, allowing the glass on top to be more true to profile, which would be (slightly) stronger, and reducing the filling requirements at the finishing stage.
The biggest drawback is that the hard-shell needs to be sanded before the layup goes on to ensure a good bond, which adds a step (time consumed) not needed in the plans method. However, done right, hard-shelling should reduce the time required filling and sanding later on, so the time spent vs saved will partially cancel-out.
Some serial builders / manufacturers swear by hard-shelling, and they ought to know!

But there are some concerns, not fully addressed in my eyes, about adhesion between the glass and pre-cured micro. There has been at least one report of glass peeling off the micro very easily, showing very low adhesion between the glass and the core. That's potentially serious. The weak-point should be foam-micro boundary, not the micro-glass boundary.

Thus, I performed an experiment. I laid up 4 plies of BID on 3 small pieces of medium density PVC foam (PVC100 I believe, one of the tougher foams we use), one with plans-method slurry followed immediately by the layup, one with cured micro sanded with 36 grit, and one with cured micro sanded with 220 grit (not 120 as marked).
Once fully cured for a few days at 30deg (C, not F. This is mertic land), I placed each sample in turn in a vice, then using pliers, peeled the glass off the foam.

None peeled off too easily, which was by itself a good result. The 220 grit sanded sample had the weakest micro-glass bond, but it was still stronger than the foam over about 40% of the sample. Not bad!
The plans-method sample was second place, close behind, with the micro bond failing first over about 30% of the sample.
The 36 grit sample had the strongest bond, failing almost entirely at the foam.

From this experiment it appears even a surface sanded at 220 grit would have adequate peel strength, being very close to the plans-method strength. I expected this sample to do much worse! I didn't even bother with a smooth-unsanded sample (unsanded) as I expected the 220 grit sample to be beyond the acceptable threshold anyway. I would not recommend hard-shelling and NOT sanding at all. That may be what caused another builder to have poor bonding of the glass.

This isn't precise science, obviously, but is a small series of data-points that have satisfied the question in my mind at least.
I should also point out that the strength of the aircraft structure is not reliant on peel-strength. However, we also don't want glass separating from cores!

I have hard-shelled the bulkheads in Chapter 4. Following two layups, I was not satisfied with the quaility & air bubbles in the layup, and elected to strip the glass off the foam.

In both cases, the glass separated from the micro, leaving the foam completely intact. I am not concerned, however for the following reasons: 
  • The layup was cured hard, but not to full-strength, so the glass to micro bond was not yet full-strength.
  • It was HARD getting the glass to separate! I did not expect the foam to survive. I am using high-density PVC for the fuselage bulkheads, not Clark foam, so the improved properties may have contributed to the robustness of the foam in this instance; Clark foam may not have fared as well.
So, I am still very satisfied with the strength of the bond when hard-shelling, and will continue to use the method. Where foam / glass sandwich is trimmed off during construction, I can continue to test strength (to destruction) of the removed pieces, thus proving even further the strength of this method. I have already done this with pieces trimmed from the seatback (lower density foam than in other tests) and the strength remains very good in that case as well.