If you have fiat money then you can buy bitcoin directly from exchange sites as I prefer to buy it on localbitcoins as it is the safest place to buy bitcoins and if you don't have capital to invest then you need to start looking for different methods of earning it and in future you can invest those earnings in trading.
one simple way is to buy bitcoin in various exchanges that are already available in many countries. but there are still many ways to invest bitcoin. I may choose to trade and buy some good prospects altcoin, in addition to buying hardware mining can also we do to invest by doing a good mining coin. Coin selection that we do for trading and also mining is one of the most important things to choose. because it can affect our future.
Obviously there are many ways through which you can invest our capital into bitcoins. You can as you said go for mining if you are capable of affording electricity bill and all the devices that are used for mining bitcoins. Bitcoins are the most easily earned via signature campaigns.