You'll need to think about four key topics:

Firstly: are you investing for income or growth? Do you need the investment to produce cash for you to live off? Or is your income covered another way, and you are looking to build up your capital.

Secondly: how much can you afford to invest?

Thirdly: how soon might you need to get at your investment? Are you sure that you won't need to touch this money for a while?

Finally: how much risk are you comfortable with? Do you want to chase higher rewards, but risk losing some of your original investment? Or do you need to be sure that your investment cannot go down in value? Or are you somewhere in the middle?