I’ve not worked in the space industry, but I think the first step would be to make sure that humans could survive the journey – I’d look at factors such as food, effect on the human body, and mental and cognitive stimulation.
The first step is to make sure humans can survive the journey there, it is at least 6 months to get there, and could be as long as 2 years! Then you have to figure our how to stop the effects of radiation on the people living on Mars. That is probably to shield them in some way, maybe even making shelters out of the stuff already on Mars. Then there are things like how to produce food and find water? and how to manufacture the things you need for a growing society. You cant take everything you need with you, it would be way too expensive.