Like any sale, it's all about building a funnel and identifying qualified buyers. The best way to do this is to ask, who do we share a similar customer with that would like to sell what they do to our users, or that our product helps improve their product.

Companies get bought when there's overlap in the customers, or you fill the white space in their strategic map so they can move faster by buying vs. building themselves.

Once you have the list, then you'll want to create a spreadsheet (hopefully you have 12-20 names) and then identify these 3 people at each company.

CEO - making the final decision.
Corp Dev - it's actually their job to buy you!
Product Manager - internal champion that will decide if you're the right fit for them.

Sometimes these can all be one person (i.e. the CEO) or only 2 people - either way, you'll want to build a relationship with each on quickly by getting an introduction.

You don't want to come off as "hey, we want to sell what we've built" but more, "hey, I think we share a similar customer base and could do something together that would be mutually beneficial". That will get you a meeting.

If you start with 12 companies and do the work, you should be able to get 3 of them competing to purchase your startup and you can use this as leverage.

The key is to get them all to the same point, at the same time (i.e. giving you a term sheet or offer). You don't want one to move to fast, and not let you get the other interest going - or they might pull out of the deal from your lack of decisiveness.

I've written about this in more depth here:
http://maplebutter.com/7-tips-for-getting-acquired/

Hope that helps.