Learn how to reach out about job/internship opportunities, follow-up on professional experiences, ask about a hiring process, and use a professional thank-you to reinforce an in-person or online connection.
Membership in a professional organization is a great way to get to know the people in your field. Many have job boards and career advice only available to members. Most have student rates.
LinkedIn is a great resource to use overall, and looking for alumni at a company of interest or in a specific position is a great place to start. Learn how to have a great profile and how to reach out effectively.