How do you easily project manage a product launch?

Short answer - Get a good project manager on your team :)

But I understand you don't always have the luxury to get a proj. mgr for a product launch. In some cases, for bigger launches, I have asked for a shared proj. manager from another team (especially the product team). If nothing - you basically have to wear two hats. I find it very hard and time-consuming because it takes me away from my PMM work, but it is a key role and someone has to do it diligently. I also use proj. management tools, don't have a preference here (asana, jira,...whatever rocks your boat)

Launches are like project plans. If you look at Engineering release plans, similar approach. We followed typical checklist - working backwards from launch d-day to the details of - web, content, PR, AR briefings etc. There is no easier way to do it, apart from a checklist so you don't drop packet. 

Research all should be done before messaging. 

Launch strategy - samething, - what is the objective, is this a new category or existing, but new product. 

Get the above all done and then build checklist. Just focused execution after that. Rallying the troops - marketing, sales, even partners etc. 

I have used a number of applications in the past to project manage product launches. You can use Trello, Kapost, or even Excel.

The key to driving sucess is alignment across marketing groups and other teams. I set up weekly meetings where we go over set agenda items and deliverables. Frequently touching base with team members allows you as the launch manager to find out if there are bottlenecks that will affect the launch.

I don't think there is one tool that will necessarily make launches "easy", but I certainly agree with Nina that alligment is fundemental towards the success of a launch. 

I have found that daily all-hands meetings with the leader of departments can be very successful in keeping everything flowing smoothly. While some may argue that this takes too much time, having the peace of mind on a daily basis that everyone is covering their bases will give you the opportunity to focus on strategy and other components of the launch. 

Additionally, I always have been an advocate for transparent accountability. This can be as simple as having a checklist on a whiteboard that is visible to the entire office. Although you never want to put someone on the spot, keeping people aware of where they stand with a product launch puts pressure on them to deliver.