Read every day. Reading expands your knowledge by exposing you to new ideas and new concepts. Your brain takes in these new concepts and synthesizes them so that you will be able to apply what you read later. Combine light reading with denser material to continually challenge your mind. Your vocabulary will expand and you will learn to make connections.
Write to further exercise your brain. Writing forces you to articulate what you have learned or are trying to express in your own words. It is like a personal review, as you convert your thoughts, ideas and emotions into more concrete forms. You can write personal letters to friends, essays for school or even summaries of what you have read. This will help you remember things better.
Exercise your body. Physical exercise increases blood flow to your brain. This helps your brain work faster, keeping you on point. You can choose what sort of exercise you wish to do. Running, weight lifting, yoga and just about any activity that will increase your heart rate is effective in also increasing your IQ.
Eat a healthy diet. Keeping yourself physically fit benefits your mental capacity. Making sure you get your dosage of daily vitamins is beneficial. Eating fish will be especially helpful as fish are loaded with the same fatty acids that make up your brain. Your brain needs energy, so make sure to ingest lots of proteins and carbohydrates.
Listen to music. The University of California conducted a study where college students listening to Mozart raised their IQ scores by 9 points. Although this "Mozart Effect" has faced scrutiny, there is no argument that listening to music stimulates your brain. It can help relax you and keep you focused, which is key to attacking challenging problems.