How do I know which gender a noun will be?

There are some suffixes which give hints to the gender.
For feminine nouns, these include: -heit (e.g. die Freiheit), -ung (e.g. die Sammlung, with some exceptions, such as Ursprung which is masculine), -schaft (e.g. die Freundschaft), -keit (e.g. die Arbeitslosigkeit), -ik (e.g. die Musik), etc.
For neuter nouns, this includes: -chen (das Maedchen), -tum (das Christentum), etc.
For masculine nouns, this incldues: -ismus (der Rassismus), -ich (der Teppich, with some exceptions, such as das Reich), -ig (der Koenig)
It should be noted, that a lot of these have exceptions, however the majority of words with these endings do follow suit.