Ask HN: How to contact someone at a company I'm applying to?

I'm a senior Computer Science student graduating in May. I've applied to a lot of companies and heard back from almost none of them. I've heard that it is much better to contact someone before applying or as you apply but I'm not sure the best way to go about this. Do I find a manager or recruiter and just email them? What would such an email say?

Any advice would be very helpful!