A very common first encounter is a meeting at a restaurant where the Johnson will offer complementary food as an incentive for the team to take the job.
The simplest way to bring player characters together, especially if you are not running a table of experienced players who have built their characters to have shared contacts or a shared history, is to simply have the Johnson reach out to each player character's fixer. Each fixer then relays the message to the PCs that there is a job offer for your particular set of skills, the meet is at location X in 2 hours.
If your group has built characters together, on the other hand, it's entirely possible they've come up with a reason for why the PCs are already established as a team. Any one of the teams fixers could offer a job, and off you go.
Another method is the tried and true "wrong place at the wrong time". Somehow, inexplicably, all of the players find themselves at the same event and suddenly all hell breaks loose. Through necessity rather than intent the players discover that the other player characters have a skill they need, and they quickly begin working towards a common goal. This one takes a lot more setup from you as GM, but can be a fun way to kick off a game with a spectacular bang.