Go Where The People Are
If you believe that all opportunities come from people, then it should go without saying that knowing more people will produce more opportunities for your career.
One of the best ways to meet others in your business community is to join professional organizations. However, there are many to choose from, and you cannot join them all.
It is best to select two or three groups and participate regularly. Often you will find people who try to attend too many events. They end up not fully engaged with any organization and thus they practice "drop in networking", and never being seen as an important member. To create bonds you must do more than join and passively attend, you must volunteer your time for the good of the organization.
Instead of just dropping in, be an evangelist for the two or three clubs that you have joined. Volunteer for the board or a committee and spend several years attending each of these groups local events. It is okay to "drop in" on other groups from time to time, but you want to invest the time to create real connections with those who are active in your same organizations.
Select the groups based on your interest in their cause. There are tons of local and national professional business associations (Chambers of Commerce, Association for Corporate Growth, etc...), civic organizations (Rotary, Lions Club, etc...), charitable groups / boards (United Way, Young Men's Business League, etc...), etc... I suggest belonging to groups that have different purposes so that you are encountering different people at the different meetings.
Go where the people are if you want to expand your professional network.
Have A Great Day.