join the organization you want to based on your needs. I'm not too familiar with the Rotary Club. All civic clubs are probably helpful in some way or another. I enjoy Toastmasters meetings, so I go to those. I used to attend Chamber luncheons, and enjoyed it, but had nothing to do with the customer base. (I didn't own a biz)
If there are any professional groups in your field, you might find them worthwhile. Any club should allow you to visit a time or two before requiring dues. There may be 'meetups' in your area.
http://www.meetup.com < Some are based on business interests. I've found it a great way to meet diverse people around town. If you're interested in metaphysical subjects, see if they have a "Law of Attraction" meetup. I've met many business owners there and everyone is there to promote themselves (and each other).
The Small Business Administration is usually a good resource. They used to have a mentor program with business owner volunteers.
Not sure the status on that program. They'll have something for you.
http://www.sba.gov/aboutsba/index.html