Annual weeds complete at least one life cycle from seed to seed during a season. These spread by seeding and all fertile soils contain a large reserve of dormant annual weeds seeds. The golden rule is that annual seeds must be removed before they set seed, thus breaking the cycle. Hoeing regularly in my opinion, is the most effective way to accomplish this, little and often.
Physical barriers such as weed suppressant membrane, organic mulch pebbles or ground cover plants are the most reliable and eco friendly method of preventing the appearance of weeds, mainly through excluding light thus preventing photosynthesis.
I personally don't head straight for the chemical weed killer as I'm all about the bees but they are effective if used correctly as per manufacturer's instructions. Organic herbicides are available on the market, and you can mix up a solution at home that is pet friendly, a solution of dish soap, salt, vinegar and water will effectively kill weeds, and plants for that matter so be careful where you spray it!