NO INVESTMENT STRATEGY!
Yeah. This one is gonna be hard :)
And take a LOT of time. I don't really suggest this path, unless you really just wanna play for months without a profit
MODERATE INVESTMENTS
This strategy will take you on ONE of the next paths. Why one? Because you won't afford more
Arena - Right now the Arena is dominated, so unless you strike a deal with the top dog, you won't be able to make money in there. Strategy is: buy weapons, keep high energy, get the bonus. But weps and energy will cost you pretty much in the beginning, till you reach a good arena bonus and maintain yourself there.
Wars - Perfect. You get the small medals really easily, and you can sell them for euros. Also, you get part of the warfund, and that is where the real money stands.
Companies - People need products....why not making some for them? But to make a good company, you might need more than just one, because there are raw materials and products. And you will need upgrades to make them cheaper than the normal one. Read more in the guide.
Fights - small amount of money, not worth it without high energy
Refferals - every person you bring to the game will pay you a tribute, 10% of what he makes or invests. Right now, this is one of the good ways to make money, since there have been people who got up to 150-170 Euros in a month by this strategy
HEAVY INVESTMENT
You can invest and buy Experience. Now your workdays are woth around 2-3 euros. It's a steady income, but combined with your companies, you can make ina day more than others in 30 days.
And also, now you can go on all the paths above