First of all, calculate how much money you have to make an investment at present and how much will you be able to invest in the future.
You have to develop your time horizon whether you are planning to invest money on short-term, medium-term or long-term basis.
Decide your level of risk tolerance. Are you a risk taker or risk averse? It is very important for you to know and understand your risk tolerance as your whole investment plan will be based on this.
Now, you have to select a diversified portfolio which is most suitable for you according to your risk tolerance and time horizon. For instance, if you are risk taker and aggressive, you should select more stocks in your portfolio and if you are less aggressive, you will be more inclined towards the bonds on which the return is fixed.
You have to examine your portfolio from time to time in order to handle your assets well. If there is a need to re-balance your assets, you must do it.