First option is always work hard on your SEO to get your organic rankings up first as that will always be your cheaper option in the long run.
Google Ads is a great additional sales channel for your website and if managed correctly will generate you the leads / conversions that your business requires. The first step is to establish if the existing site has the necessary content and landing pages in place to make sure that you convert as many clicks as possible and to reduce the budget destroying bounce rate. A conversion could be a telephone call, a contact form completed, a webinar registration, a product purchased…
Make sure that the site has Google Analytics, Google conversion tags installed so that you can measure the effectiveness of your campaign.
With these measures in place then you start your ads which might be a single campaign or better still a series of campaigns and ads based on your keywords selected, location to display ads, devices and other adjustments that may be applied.