The fact the econ and industry simulation manages to be challenging even in singleplayer mode is probably a big part of why so many of us keep coming back to SR series. Here is general strategy and it has worked playing various titles in the series and with starting positions that include: Egypt, USSR, USA, Germany, Ukraine, Botswana, and Spain.
1. Decide who your "friends" are. These are regions who either (a) have a geopolitical position that can benefit you (the relationship Russia and France had in their late 19th century alliance is an excellent example of this, as was the British Portugese alliance that existed at certain points), they might also be (b) trading partners who can provide non-trivial quantities of resources you need. These will invariably be regions you do not intend to antagonize and wish to inculcate the strongest possible positive relations with. Do not attempt to make this list too long; spend a considerable amount of time deciding who is on this list and make sure there are no redundancies. You will need to accept many compromises and tradeoffs in order to foster the advantages that these relationships can afford so choose well.
2. Everyone else is either a potential victim or just a nobody. Decide who the potential victims are. Again, don't go overboard. Having only one or two "potential victims" (PV) in mind at the outset is perfectly fine. You may not provoke hostilities with anyone for decades, but it is still good to know whom you are likely to be fighting eventually and for what strategic advantages. It probably goes without saying that PV should be nations which provide some uniquely valuable and critical asset to your nation. One of the beauties of SR series is that most of the modern world critical strategic assets are well-represented and depending on your starting location, there is no way of knowing what those critical assets will be, but you need to decide what they are. For example, playing Germany 1936 scenario: Petroleum is the overriding mid- and long-term strategic imperative. Acquisition of as many and as high-quality of petro product hexes should be Germany's primary objective.
3. Now that you have a mental image of your strategic ecology and which direction you need to be moving through it take some steps toward "clearing the slate" on your existing economy and industry:
a. Unreserve all military formations and move them all to one central location. It is not essential that the Sea Port, Air Base and Barracks these go to are all in one hex, and in fact centralizing ALL of them can be a bad thing depending on your nation historical period, etc. But I consider "centralizing" all forces to be the standard and any deviations from that only on a case-by-case basis.
b. Deactivate, if not scrap as many of your airfields, barracks and sea piers as you can withstand. Again, doing this at all might be a VERY bad idea, but analyzing one's situation from the standpoint that "pruning" the military infrastructure is the standard "best practice" but stepping back from that imperative as appropriate to the situation.
c. Go to military minister and turn him off controlling anything; in fact, you are going to do that with ALL your minister save perhaps the finance guy, who will only stay "in control" for a brief period of time until after your economy stabilizes from the austerity measures . . . reduce military salaries and maintenance by about half (once again, DON'T do this if you are playing a region that is just about to be in a war . . .)
d. Set up your Research queues manually (turn off the stupid Tech advisor thing) and set the rates to your needs. Generally, I think it is a good idea to maximize research, but that can vary a lot.
e. Go to your State guy/gal and turn down espionage and other sundry funding by about half
f. lock the production minister out of EVERYTHING. Turn auto sales and auto purchases for everything completely OFF. This is tedious, but basically, for the sales page, slide the quantity sliders to zero and the minimum price slider to max. For the purchases page slide everything to zero.
g. Crank up domestic prices to 200%. We don't want inflation, and we want to know what our maximum flow of resources is WITHOUT the population eating more than they absolutely need.
h. Deactivate ALL production facilities (keep in mind, this is all being done while you are in pause mode and the game has JUST STARTED! trying to do this even while the game was on Very Slow would be horrific).
i. Turn on your supply map and spend some time browsing through your resource tabs and looking at the locations of your existing facilities relative to the supply distribution.
j. Start one or perhaps two supply depots at the ideal location. Generally this will be the capital but it might also be a seaport. A capital seaport WITH an airport is the ideal!
The goal here is to create an initial zone of MAXIMUM supply. Turning off everything and sending the entire military into one central reserve point AND deactivating military production if that is not suicidal are all part of this plan.
Ideally, you want a "central" high pop hex which already has relatively high supply (generally the capital) where you can fit an airbase, a seaport and a supply depot. As far as I know those are the three initial facilities in most all the scenarios and titles that boost supply and boosting supply is the first step to building an efficient and killer industrial sector, which is the first step to building a killer economy.
k. You can leave the finance guy running for now, and perhaps even set him with some directives that can assist with the current measures being taken, but I suggest deactivating his control over facilities construction and repair.
l. In case it isn't obvious by now, also deactivate all garrisons (if tenable), turn all "initiatives" of units to zero, and otherwise turn off ALL "auto" features within your national and military institutions. You want (at least for the initial weeks and months of play) to have complete control over everything and NOT be fighting with the computer "helper."
I may have left out one or two specific measures that fit under this category but you get the picture I reckon: downsize, deactivate; only scrap if you are confident you don't want don't need, and with "airfields," sea piers, and even barracks I find they utility at the outset of most scenarios is not worth their maintenance costs. Scrapping other types of facilities that are in remote regions, plopped on top of a resource hex which they block, etc. can be good.
Oh I almost forgot! Scrap all the mini-, micro-, and mid- versions of all your production facilities. These are inefficient and useless. Build ONLY the largest available sizes for all those facilities which have alternate sizes.
4. Let one day pass in order to process all the changes you've made and pause it. Now you can see "where you stand" at base level: How much food and timber is being produced even without any facilities on? What is the economy like with domestic consumption strangled to a bare minimum? How far short are you on all the things your region is inherently consuming? Now comes the tedious part, and the part where I feel BGs User Interface is the most deficient . . .
5. The goal now is to activate the MINIMUM number facilities necessary to keep your nation "afloat" while your supply levels build up and your first one or two supply depots are finished. The ideal here would be a button on the pane where one can activate/deactivate facilities that allowed the user to sort the order in which facilities were serialized according to one or more parameters. For example: Sort High to Low Supply, then click click click to activate a few of whatever facility you think is enough, move on to the next <--- that would be the ideal, but unfortunately the UI doesn't provide that feature so the only option seems to be to go back and forth between the Land tab and the production facilities tab so you can highly where they are and use the supply overlay to eyeball which ones to click on and select.
Once you think you have reactivated just enough of the facilities that are in the best supply situation, then let another day pass. If your existing stockpiles allow it, then it is ideal to just run forward in time to the point where your initial supply hub(s) are being finished before reactivating anything.
That pretty well covers the most esoteric aspects. The key take aways are that: I. Supply is crucial for everything in SR; II. For facilities like industrial, and commercial goods, efficiency and productivity seem to gradually climb the longer they have been online, the upshot of this is: once you've done this initial "clearing the board" measure, you ideally don't want to ever be deactivating these facilities again; III. Facilities in "low supply hexes" (e.g., < 75% supply) are honestly not worth running. Facilities in really low supply hexes (<50%) can honestly do more HARM to your economy than good. Scrapping them should only be done if you are confident they will remain a backwater for a long time, but deactivating has few long term consequences if done right at the game start before supply has become distributed and efficiency has started to increase.