Actually it depends on you how much money you'll going to invest. You just follow this motto and you'll be good "The more you invest, the more profit you will earn." but if it's your first time investing and don't have enough knowledge about what are you going to enter i may say that you should just invest a little amount in order to have a experience and familiarize about the things.
Remember that investing into something is not a joke it may lose all your coins in just a glimpse of an eye so make sure that you're aware of the risk in investing make sure you've made a research and know the cons and pros. Make sure that you can afford to lose the money you invested.
Investment can be consider as passive income, but still to find a profitable business where you can trust and invest your assets, you need to have good experience and study. You will like to invest your money in such place where your money is more safe, but it is not so easy to find such business where you can put more and more of your money . for this you need to study the market and choose the best place for investing your money.