The form of marketing is dependent on two major things:
- Stage of the customer journey (Awareness, Interest, Desire, Action)
- Stage of your startup
If it is an early stage startup, the main motivation for marketing should be creating awareness about the venture. At this stage, it is best to grow organically, instead of having paid ads or buying keywords for SEM.
Content Marketing and growing through referrals is best at this stage, since these methodologies entail negligible costs, and are great tools for generating leads.
Since you are trying to generate leads for a dental clinic, it makes sense to have content pertaining to your field posted on Facebook groups and other social media platforms. Collaborating with dentists and having them share your content would also work in your favour. Most importantly, you need to have a call-to-action button, that can take a reader to a landing page, wherein he/she can drop their Email IDs for further information. These are your leads, who have now progressed onto the second stage of the customer journey, the Interest stage.
At the Interest stage, Email Marketing is a very good option, wherein each lead can be sent personalised mails highlighting the services being offered by your venture. The Call to Action button could be a link to your website where they can access the services.
Once your site has enough traffic (which you can measure through Google Analytics), the next step is to focus on Search Engine Optimisation (SEO) and Search Engine Marketing (SEM). SEM can be expensive, so you should be very careful while selecting the Adwords. Put yourself in the shoes of the customer, who is now at the Desire stage of the journey, and figure what are the words he/she would type in the search engine while looking for services.
Hope this helps.