Specifically this is all from the perspective of the major scale, even if you don't ever actually end up using the I chord (i.e. the end result isn't in major at all) in the process of all this - it just serves as a means of keeping track of which chord goes where.

That said, yeah - chord substitutions. Basically, you can just subdivide chords into a particular class that determines where in a given progression they would typically go; a la traditional functional harmony these would be tonic, subdominant and dominant, though I'll be using them kinda differently here - mostly because generally speaking the first chord in the progression, regardless of what class it's in will be the one that feels like 'home'. That said, the vast majority of progressions in popular music tend to be either tonic-tonic-subdominant-dominant (a la classical functional harmony, also the so-called '50s progression common in a lot of pop music from the mid-20th century), tonic-subdominant-tonic-dominant (a la the ol' Four Chords of Pop and its variations), and tonic-tonic-dominant-subdominant (a la the Andalusian cadence {sorta}, also employed in blues music and its direct derivatives).

Now, as to what goes where? The tonic chords are fairly straightforward - the diatonic ones are just IMaj, VImin and IIImin - the root notes of Ionian/major, Aeolian/minor and Phrygian respectively. Those aren't your -only- options however; personally I've found VIMaj and Imin do the trick just fine. IIIMaj not so much, though - more on that in a bit.

Next, the subdominant chords. Your primary options are IVMaj and IImin again, though this category is a pretty big and loosely defined one - it's only really defined by what it *isn't*. Here we see a rule of thumb that we'll also see back more definitively for the dominant chords, which is to say you can, for the most part, substitute these with their counterparts either a minor third (in either direction) or a tritone away; given that IV and II are already a minor third apart, this basically just means any major or minor chord on II, IV, bVI and VII. Augmented chords work well here, too - on any note at that, though given the fact they're technically on three degrees at once unless you venture outside 12 tone equal temperament (at which point basically all of this starts to fall apart anyway) that list exhausts all your options for those too unless you want to strictly define a root note for it through voicing. Other than that, if you're feeling -especially- weird... honestly, you can probably use literally anything that doesn't fit the bill for the other categories, but you'll have to play that by ear.

Finally, the dominant chords. VMaj and VIIdim diatonically, and six more options that while they don't have quite as much potential to feel like 'home' in a chord progression in spite of starting on them, will work just as well for the function's sake as far as I've been able to glean. Again, anything of the same chord quality that's either a minor third or a tritone away (the ol' tritone substitution) will work for this. This leaves you with VMaj, bVIIMaj, bIIMaj and IIIMaj, as well as VIIdim, IIdim, IVdim and bVIdim. Some of these will sound very familiar; of the major chords (often extended to dominant sevenths in practice) only IIIMaj isn't commonly used, and VIIdim and IIdim (often likewise extended to dim7 or m7b5) both have their place especially in older songwriting.

I suppose this same concept -does- hold up for tonic chords as well to some extent, but only if you ignore IIImin for the purpose (bIImin, Vmin and bVIImin don't exactly sound like tonic chords, lmao) and if you don't do this with the starting chord - there is a need to keep things rooted one way or another, here.

I suppose there's more systematic ways to go further still by extending stuff to seventh or even taller chords for instance, but I -really- haven't done enough research to go about explaining how to do that reliably for all this - shit's gloriously messy at the end of the day, and what really matters is what works, first and foremost. Even this doesn't exhaust every chord progression that sounds nice by a long shot (and indeed, some of them get pretty weird especially when you venture super deeply into chromaticism); it's just yet another system out of many.