I started in business 7 years ago . I had the same questions that you have , and I didn't want someone to tell me " Know your costs " . Honestly , you really need to know what it costs you to be in business . Many people start in business thinking they are making money until the suppliers are due , then "Oh S___" how will I pay this . Others go along fine until taxes or insurance come into play .
I did it the hard way . If you do , I suggest start with small jobs , that way if you don't bid enough you won't go bankrupt . You will probably bid some too low in the beginning , I certainly did , I still do sometimes . It helps you learn quickly .Also it depends on what end of the business you are in . Right now I am sticking to Service calls ,because the market is so competitive on most everything else . Unfortunately it usually takes a few years of word of mouth to be able to do that , plus advertising .If you are planning to make a living wiring houses in this economy , good luck . Even small commercial jobs are pretty cut throat right now .
I wish you all the success in your endeavor .
Overhead + Profit + wages = hourly rate