If you are a Candidate Looking for Job , You should connect to HR professionals of companies (Make a list of your dream companies first), Recruiters and Agencies who are looking for candidates in your Industry. You can also try and connect with employees of favorite company and can earn referrals.
TIP : If you see a 3rd degree connection and you are not able to connect , LinkedIn will let you connect if you know any 2 credentials of the required 3: Company Name , Email Address , Full Name , where as email addresses of professionals are hard to find on Google but you can search full names easily and connect 3rd Level connections easily for free.
Social Marketing Professionals with responsibility of marketing should outline their target industry and try to connect with professionals working in that vertical. Generating direct business on LinkedIn is not an easy task , its a brick by brick process. You have to connect, grow, share and gain trust of professionals.