This can be an effective way to grow revenue or build awareness for your business. The most popular and effective options are using Google Search or Display advertising and Facebook ads. Both of these have extensive targeting options to reach your ideal customers. You can target by geography, age, demographics or even people that have visited your website or a particular section of your site. Think about the value of your add showing up in search exactly when your target prospect is looking for the product or service you offer!
If you are tech/marketing savy enough you can study up and implement these tactics on your one. Otherwise you could be time and money ahead to work with someone that already has the expertise and will be effective. You can set budgets on what you want to spend to control your cost and increase your budget as you see results.