Well, it's up to you what to produce. You'll want to be able to upgrade your city a lot to increase population growth, and that takes tons of cement, lumber, and steel. I've been spending tens of thousands of steel on my city upgrades. Even though I have over 2.5k steel per hour production I'm still using it all up upgrading everything.
When building supplies are scarce you'll want lots of low level buildings since they produce more per resource invested, but later on you'll want fewer higher level buildings to better utilize your workers since the higher level ones are more efficient per worker. Thats why my focus has shifted to upgrading my higher level buildings even higher, but I'm limited by total workers.
My own strategy was spam tons of lumber/cement buildings for the first week or so, upgrading them as I could, just to get enough building supplies to branch into other things. I started with steel producing buildings after a few days when I had some extra materials, to get steel production started off. After the first 6 days I think it was I stopped upgrading some of my buildings (the level 12 ones) to eventually demolish them, since you have to demolish 1 level at a time. I started to hit my population cap the last few days, limiting my upgrading, and I've taken down 7 of the level 12 buildings since yesterday and replaced them with other buildings (rubber production, and some buildings to satisfy the missions - I'm aiming for the city missions, since they give lots of new people).
That strategy was born out of a serious lack of raw materials though. If I can get this train in a reasonable time frame I could boost your development quite a bit with a few train loads of raw materials, which could probably get you to the point where you're utilizing all your population much faster and wouldn't have to rely on tons and tons of low level buildings to get started. I don't know how long the train will take though, you might be better off just focusing on doing it yourself for now lol...
I'm hoping to have excess steel production soon as well, but like I said so far my upgrades have been sucking it up as fast as I produce it.