Part of shifting that momentum comes through highlighting and internally publicizing early post-integration wins or other instances of employees from both companies working well together. Warren said this can help to get all employees on board with the integration. 

Companies can study the strategic or technical fit of a potential suitor before deciding whether to proceed with a deal, Warren said, but the one component that eludes measurement is company culture.

Warren urged businesses interested in M&A to ensure that the cultures of both companies align before agreeing to a deal.

"It's really hard to change culture," he said.  

Businesses should have a detailed plan for the first 90 days following the close of a merger or acquisition, Warren said, allowing the combined firm to gather enthusiasm and momentum as key milestones are achieved.

A well-planned and well-executed integration should take about six months, Warren said. Companies should only pull the trigger on a deal if they think they can get a full return on their investment within five years, he said.

Warren encouraged companies to bring on third-party consultants such as Revenue Rocket to mediate differences between the two sides as the integration process progresses.

The advisor should play the role on the bad guy, Warren said, delivering the news when one side of the combined company isn't going to get its way so that resentment doesn't build among the active workforce.  

Integration poses a particular challenge to companies with annual revenue of below $2 million, Warren said, since processes for firms that size are often in a particular employee's head rather than being standardized or written.

Documenting the processes is probably good in the long-run though, Warren said, to avoid gaping knowledge holes in the event of employee turnover.

The cheapest way to acquire another company is by paying all cash, Warren said, and he recommends putting down as much cash as possible if the buyer is confident that the transaction will be a good cultural and strategic fit. 

But in reality, Warren said 90 percent of M&A deals have some sort of payout to ensure that the selling company has skin in the game after the deal closes.

This minimizes risk for the buyer, Warren said, but limits their upside and can ultimately result in them paying twice as much as they would have in an all-cash deal.

Brian Quinn of Wholesale Computer in Monroe, Conn. said he has begun thinking about selling his company since he is 50 and his business partner is 55.

"Some point in the next decade, we need to have an exit strategy," Quinn said.

He was particularly interested in what Warren has to say about how buyers can save money by paying entirely in cash as well as the importance of cultural fit in ensuring a successful integration.