Best advice I can give for a mining town is to use it as a foundation and eventually push into the only lucrative money making export in the game, tv/computers! The biggest bonus of starting with a mining town is gaining access to alloy. This allows raise your profit margin later on by lowering your import costs, making all the alloy you will need. Using this strategy Ive made several cites that make over 7 mil a day and can easily support a great works solo.
To start you keep pushing mines! With a combination of coal and ore, 5-6 mines and 3 trade depots seems to do the trick for me. Its important that you are not wasting output. A mine working at full potential will do 120 tons a day. 3 trade depots exporting both coal and ore full time will do the trick. At this point you will probably see trade numbers of about ~300k exports between ore and coal. Not to mention you have probably made sufficient cash to support a majority services. No education yet.
With these mines you start saving for the next breakthrough. Your aiming for the first upgrade from the Metals hq, you want to unlock smelting asap. Dont worry about Trade HQ yet, that's the next step. Ploping a smelter is the next priority, again were aiming for alloy here, so always demolish the metal smelter that comes with the building and just add on alloy. Make sure at this point each of your trade depots have 1 storage box of each alloy/coal/ore. Don't worry about your current smelter not having enough resources, you should be exporting everything. You should start making good money at this point. Upgrade your smelter with 4 alloy addons before the next step! Once your smelter gets to work you should see trade profits per day of about ~400k from alloy ~250k from ore/coal.
Plop the trade HQ. You should be exporting enough at this point to get an upgrade here off the bat. Plop the metals division when you can. BOOM now your ready to move onto the "bigger" trade ports (cant remember the actual name so ill just call it bigger for now). You want to make sure these bigger trade depots are nearby sea or rail (or better yet both, a single trade depot can make 1 freight rail and 1 freight dock). These trade depots are extremely more efficient and they export in larger quantity's (100 tons at a time) as long as your using at least one of the sea or train attachments. Agian have everything on export at this point (coal/ore/alloy). After your trade depots start exporting efficiently get a second smelter going with all 4 alloy addons. Let it work for a day or two and at this point you should be roughly making about ~800k from alloy and ~200k from coal/ore.
Now you need to get recycling going before you make the next jump. You should have plenty of money at this point to really do as you please. Plop a recycling building with the plastics add on (comes with it). The recycling center might not be doing anything at this point but the key is just having it. With the recycling center your "smaller" trade depots should be able to plop plastic storage.Dedicate an entire "smaller" trade depot to handling plastic (all 4 storage nodes) and set to use localy. Let the plastics build up, for now.
Next you need to unlock the option for processor factories (5 high tech industrial buildings). With the exception being the grade school, education of any kind will give you factories you need to unlock processors. Build a processor factory. Now we need to make some more changes to the "smaller" trade depots. Go to the smaller trade depot you made earlier with plastics in mind, and set to import. As you cant use the larger trade depots to export processors yet, redo another smaller trade depot to solely export processors (using all 4 nodes of storage for processors). Also max out your first processor factory with all 4 nodes pending some simmillions is coming in. At this point your "bigger" trade depot is doing the work of exporting alloy/coal/ore, while one "smaller" depot is exporting processors, and another one importing the plastics. Don't worry about running out of material, set all ore/raw/alloy/processors to export. After a few days you should see numbers of about ~900k from processors ~750k from alloy ~200k from coal/ore.
The next goal is to be able to export processors/tv/computers from the "larger" trade depots. Build another processor factory as you will need 2 fully maxed out to supply enough processors for your tv/computer factories later on. Also plop the electronics HQ. The second factory should skyrocket you to the 2nd upgrade at the trade HQ. The next upgrade here will be the electronics division. Once you have this you can plop processor storage units at the larger trade depots. You will see a dramatic increase in profit after this. ~2M from processors ~700k alloy
Upgrade your electronics HQ first with the TV headquarters first. Start making tv's/computers and exporting them out from the bigger trade depot (remember to plop storage units for tv/processors). You should have no problem unlocking the last upgrade for the trade headquarters, making the plastics HQ will allow you to import plastics. At this point you no longer need the smaller trade depots and can demolish them entirely.
My final town contains 3 tv factories, 2 processor factories, and 1 smelter. I normally have at least two big trade ports going(3 if I have industry that needs freight) . Each exporting processors/tvs/computers, importing plastics, and alloy on use locally. The 6th spot will be different between the two trade depots, one importing ore and one importing coal. You could potentially keep on building factories to boost profit but at this point you will be making more money then you can spend ~4M tv ~4M computers ~2M processors . Also you might be thinking at some point how you fit all this. To help with room, somewhere inbetween the switch from alloy to processors I normally demolish all my mines and begin importing coal/ore. Importing coal and ore are pennies compared to the price of directly importing alloy directly. Enjoy and happy building!
TL;DR - MORE MINES!