Cross-selling is DEAD! At least in the way that I have heard it defined for many years. That definition is attempting to get lawyers of one discipline or practice area to pro-actively sell additional firm services to a client.
Certainly a firm would like to work with a client across broad legal areas, but the old-school practice of cross-selling is so backwards. Essentially an attorney is asked to sell a product (another legal specialty) they don't know.
Why not turn the process around and enable opportunity to happen organically between attorneys at your firm.
What does work is "client teams" meeting regularly to discuss the business issues of a client. Team members are attorneys of different disciplines meeting to analyze the business issues of a client and brainstorming real solutions to difficulties that actually exist. Then, the client is offered something USEFUL and relevant to their business.
Cross-selling is saying to the client, "If I introduce someone to you would you consider finding work for her/him?" Client teams say to a client, "I've formed a brain-trust around YOUR business and YOUR issues, and we've uncovered some ideas for your business that could go right to your top-line."
Cross-selling is negative, stressful, and unwelcome. Client teams are fun, energetic, and enabling! YOU PICK.