Choose a well-connected and respected personal manager.

 Great artist managers are becoming a thing of the past. Self-management is always a valid option in the developing stages of establishing your career as a musician. Much can be learned by taking on the jobs of securing gigs, getting some publicity, planning tours, dealing with personal issues that arise within the band, and schmoozing with A&R Reps and various other label and publishing personnel. However, there comes a time, usually when the daily tasks of doing the business of being a band takes up too much time, and it is at this time that the services of a good manager can be very useful. I have always felt that if any musician or band has worked hard to establish their career, and achieved a modicum of success, they will have a better chance to "attract" the services of a professional, well-connected and respected manager.
Managers who do this job for a living can only take on clients that generate income. Making money as a personal manager is no easy task, and many upcoming artists forget that if any monenies are to be generated from their music, it can takes years for the flow of that income to be reliably there. So, as a band develops self-management, or gets help from intern/student manager-wannabees, this can help pave the road for professional management.
Over the years I have heard several horror stories about "managers" that approach upcoming acts and say that for X amount of dollars, they can do such and such for the artist. No... this is not the way legit personal managers work. Well-connected and respected personal managers get paid a negotiated fee for their services (get it in writing) for any and all business transactions they are responsible for (15%-25%) over a particular contract period. No musicians should ever pay a fee to a so-called "manager" who will not do any work UNLESS they are paid up front. Flim-Flam men and women still abound in this business... be forewarned.
One of the most important jobs of a manager is to secure recording and publishing contracts for their clients, this is why it is so essential to choose well connected and well respected managers. The music business is a "relationship" business. Who know who, and who can get to know who, and who did what successfully for who... is what this management game is all about. Choose carefully those people who will be representing you in any business dealings.