I am now scrapping all petrol power facilities.
That right there is one of the first things I suggest everyone do. The more petrol plants you start with, the greater the savings after you scrap them. (Note: I always scrap so that I get back the materials used in making them) I detailed the effect in one of my AAR's. I think coal is the best early power if you have adequate resources, its cheap and does not take very long to build.
This is not for all and some will disagree but, my main income is domestic sales. When you have the correct "balance" of taxes and social spending your people are willing to spend more on items.
(Note: I have not seen anyone ever post this but in my game experience it is true. When you play with random events on, if you have a balanced set of taxes and social spending the random events are positive. i.e. extra petro due to less wastage in conversion, extra money in the treasury due to an audit discovering an error in your favor etc. When you have low social spending events are negative. i.e. money stolen from central bank, etc etc.)