The way to plan it out is to decide on what you want for a target compression ratio, then see what it takes to get there.
First let me say that this whole topic tends to devolve into a religious war any time it comes up. There are people who can and do push these limits successfully, but doing so requires everything to be perfect and the engine constantly kept in perfect tune, cooling system optmized, planets aligned, animal sacrifices made to the appropriate spirits, etc.
What I'm going to give you are guidelines that I have found and also believe to be reliable, but I won't get into an arugment about them.
If you're running iron heads on 93 octane, then your target compression ratio should be in the vicinity of 9.3:1 to 9.5:1 (with closer to 9.3 being preferred).
With aluminum heads, you can (and should) run more. Somewhere in the neighborhood of 10.2:1 to 10.5.1. Aluminum is a better conductor of heat and tends to pull heat out of the chamber, which lessens the tendency towards detonation and also has a negative impact on combustion efficiency (you lose more energy to waste heat instead of using it to make power).
Zero-decking the block is a good thing to do for several reasons: it "hides" sharp cylinder edges that tend to form hot spots that lead to detonation, and it also promotes cylinder turbulence (due to the quench pad area) which keeps things nice and mixed, promoting an even burn. Zero-decking the block also raises compression ratio, so you have to know "going into it" whether you're going to have that done. (In order to get an accurate compression ratio you have to know what your deck clearance is NOW anyway - which means you've got to pull the heads and maasure it.) Pontiacs "usually" have the pistons "about" 0.020 "down the hole" when the piston is at TDC.
You also need to have accurate measurements of combustion chamber volume. Don't assume your heads are always going to have volumes that match factory specs. The volumes vary even on untouched heads, and the heads may have been milled. Even 2 or 3 cc's makes a difference.
You also need to know the bore size on your engine - what it actually is.
So with all that (did you get the point about needing to measure everything on YOUR engine?) If we make some basic assumptions which are:
389 Pontiac, bored +0.030
Standard stroke 3.750
Head gasket compressed thickness .045
Head gasket bore size 4.160
Deck clearance .020
Chamber size 69 cc's (usual for 389 D port heads)
Flat top pistons, 6 cc's in the valve pockets
That puts your static compression ratio at 10.06:1 --- too high for iron heads on 93 octane.
If we take the same parameters and ONLY change the heads, install 72cc aluminum heads, then you'd be at 9.76:1 --- safe, but actually too low for aluminum.
Keep the aluminum heads, zero deck the block: 10.187:1 --- dang near perfect PLUS you get the added benefit of improved quench from the zero-decking operation.
Lots of ways to skin this cat depedning on your other goals and constraints. For instance, keep the heads you have, don't zero deck the block, swap pistons for a set that have 14 cc's of D-shaped (D-shape VERY important) dish, and you're at 9.31:1 with iron heads --- again, dang near perfect for iron heads and 93 octane - AND - the engine still looks 100% stock (but probably won't make as much power as it would with aluminum heads)
One final thought: "Walking the razor's edge" on compression ratio in a street engine, in my opinion, just isn't worth it. On my 461 (which runs high 11-second et's in a 4000 lb car), the power difference between 10:1 and 10.5:1 would only make about 8 HP. Not worth the risk to me. Now if it was a race car and I was searching for every last smidgen of power, sure (but it'd be on race gas too), but in a street engine? Nah.