While skeptical of mergers (see below), I'm also of the view that "chance favors the prepared," and that:

• having a clearly articulated and fundamentally sound strategy going in;
• recognizing and confronting with clear-eyed vision the issues surrounding management, compensation, and client conflicts; and
• having a road-map, if not a GPS system, towards integrating the totality of the two firms' systems (including financial, time-keeping, case-management, knowledge management, document management, CRM, etc.)

can take you a long way towards success if a merger is in the cards for you.  This backgrounder about the Goodwin-Procter/Shea & Gardner merger amplifies these points.  How specific should your plans be?  Quite.  For example, it's nice to say that because you're a Washington, DC powerhouse (Shea & Gardner) you want a firm that's not, but let's get down to the nitty-gritty:  In this case, S&G was strong in litigation ("don't need that") but lacked an intellectual property practice ("expensive to build"), so Goodwin-Procter or its ilk already fit the "identi-kit" of a potential merger candidate.  But beyond the strategic fit, personality issues and communication, as always, are key:

• teams of lawyers from both firms must sit down with key clients and assure them that quality of service will remain unchanged, and explain the reasons for the merger;
• everyone from both firms on a client assignment must know everything about that client from both sides of the pre-merger firm—the client assumes and expects no less;
• on new assignments, staffing should self-consciously include attorneys from both firms from the beginning; and
• don't overlook the staff—this is a merger not just of lawyers, but of paralegals, secretaries, the back office, etc.  Send them on trips to meet their new compatriots at the counterpart firm.

And, with that advice, go into a merger with your eyes open.  Consolidation is here to stay.  Make it work for you.