10 Tips for a Healthy Diet

The Nutrition Source of Harvard School of Public Health makes the following 10 recommendations for a healthy diet:

Choose good carbohydrates: whole grains (the less processed the better), vegetables, fruits and beans. Avoid white bread, white rice, and the like as well as pastries, sugared sodas, and other highly processed food. Limit the intake of sugar.
Pay attention to the protein package: good choices include fish, poultry, nuts, and beans. Try to avoid red meats.
Choose foods containing healthy fats. Plant oils, nuts, and fish are the best choices. Limit consumption of saturated fats, and avoid foods with trans fat.
Choose a fiber-filled diet which includes whole grains, vegetables, and fruits.
Eat more vegetables and fruits—the more colorful and varied, the better.
Calcium is important, but milk is not its best or only source. Good sources of calcium are collards, bok choy, fortified nut milks,  and beans.
Water is the best source of liquid. Avoid sugary drinks, and limit intake of juices, milk, coffee, tea, artificially-sweetened drinks, fruit juices, milk and alcohol are best consumed in moderation.
Limit salt intake. Limit salt / sodium consumption from all sources and ensure that salt is iodized.  Choose more fresh foods, instead of processed ones to avoid hidden salt.
Moderate alcohol drinking has health benefits, but is not recommended for everyone.

Other than nutrition, you need frequent physical exercise and maintaining a healthy body weight. Eat roughly the same amount of calories that your body is using. A healthy weight is a balance between energy consumed and energy that is ‘burnt off’.