Surf many internet sites, read newspapers and good magazines. Read books on general knowledge e.g. Manorama which is published annually. Readers Digest is one of the best magazines. Read \'Wisdom\'. To remain up to date with the current affairs, watch TV channels like BBC, NDTV and other news channels. Also watch National Geographic, Discovery, Animal Planet for knowledge on wild like and other rare natural happenings on earth and other planets. For sports, watch Star Sports, ESPN etc.
Last of all, discuss things with senior persons, people who have knowledge, and last of all keep your ears and eyes open to know what is happening around you.
All this will help you to get updated with current affair and general knowledge.