Go through the process a user would to use your service, starting from your homepage. A typical user flow with two different target customers could look like this for a hotel. There are several different steps and then sub-processes that will require their attention and each of these two different users will have different needs/expectations going in.

What are the steps they go through and when is it appropriate to ask them to "share"?

Stepping outside the "hotel" box for a minute, airbnb has done a very successful job of building community directly into their app and experience.

When searching for places, they often have visitors guides available to help you adapt and get the most out of the city you're going to (at the top in the blue).

They also entice you to connect with a social media account in order to make your experience more intimate. Look at this call-to-action for connecting with Facebook:

Use the Notes section to brainstorm all the points you could insert social into the experience.