Some methods to help increase intelligence include seeking out novelty, seeking out challenges and social networking. While intelligence is often thought of as a fixed quality, exposing the brain to new situations and challenges can help improve cognitive function.
Seeking out novelty means continuously experiencing new activities and exploring new realms of knowledge. Many of the greatest minds in history were polymaths who sought out a wide variety of knowledge on a range of subjects. New experiences create new synaptic connections, which increase neural activity and improve brain function. Whether it's a new outdoor activity or a different genre of book, variety in experiences can help improve intelligence.
It's also important to continuously seek out challenges for the brain. Supposed intelligence aids such as Sudoku or other brain games are useful to improve thinking skills, but only until the exercises become familiar. Once the brain learns how to play the game efficiently, new learning stops and intelligence stagnates. Rather than sticking with one exercise, move on to new, less comfortable challenges frequently.
Networking with others also offers a multitude of opportunities to increase intelligence. Associating with a wide social circle increases the amount of new experiences available and thus provides increased opportunities for learning. Networking also offers new perspectives, new ideas and new challenges that would otherwise be inaccessible to an individual.