What are the top 3 priorities for a successful product launch, that hold true for all types of products?

Great answers all around. Here's what I'd add:

* You deliver a product/feature that people actually want
* You position your product in a way that gets the right people to try it (which they then adopt because of pt 1)
* You deliver against whatever higher level objective you’re trying to achieve for your company (increased ACV, capture new market share, increase conversion rate within current market, etc)

BONUS: you learn something you can apply to whatever you launch next

PS note on pt 1: you’re less likely to deliver on this unless you’re working upstream and sharing market insights with your product team. Great product marketing influences roadmap, which leads to great launches.

• Test, learn, and validate
  Formulating the foundation of your launch plan purely on an educated hypothesis is an OK starting point, but going to market on one is incredibly risky. Being a product marketer in 2021 means you have access to a variety of third-party or in-house tools to help test and validate the core components of your go-to-market strategy with end customers, including value propositions, positioning elements, and key messaging pillars. I typically like to run as many rapid-fire qualitative feedback sessions in a condensed time period as possible, and then validate those findings at scale with a fast-follow quantitative study.
• Be comfortable with an iterative launch plan
  When I’m writing the product marketing brief that will ultimately become the launch plan, I rarely get it right on the first draft. I like to involve other cross-functional collaborators (PM, Sales, Design, Research, Legal, etc.) early in the process to pressure test my assumptions and ensure we’re all aligned before the plan becomes solidified. Investing in this upfront will save you from a scramble drill as you approach launch day and ensure you have plenty of runway to make pre-launch modifications based on key stakeholder inputs.
• Have a clear path to measuring success
  Clear-cut KPIs and agreement on the timing in which you achieve significance in those metrics will be integral in determining whether your launch was a success. I like to partner with data science and engineering to build both the tracking mechanisms that power the marketing funnel like UTM parameters and deeplinks, as well as the dashboards and reporting that ultimately tell me if our tactics are impactful on launch day and beyond.

I only have one that I can think of that holds true for all types of products:

Write a mock PR to have a clear understanding of the message you (and your team) want to land.

Ah-ha moment: Your mock PR can be over the top! Do a kick-off and readout your PR with superlatives galore. Shoot for the stars! Write something that legal will DEFINITELY not approve - the best this, the most amazingest that. Use the PR to get your GTM squad excited... the review cycle will water it down, but at least you'll get your team pumped. Just give your PR team a heads up so they don't have a heart attack. 

Revenue, revenue, and revenue. 

Assuming the product is launched to generate revenue. Not all are. Some products are launched to test ideas, some might exist simply to check a box with influential audiences, others might be there to block or signal to the competition.

There are also different metrics that should be considered at different points in time and are dependent upon your business model. Obviously, revenue is not solely attributed to a successful launch. Lack of revenue certainly can be, though. 

Long answer: the question seems designed to get crisp, actionable responses but doesn't lend itself to that. 

Not all relating directly to PMM's role in a release, but should always be on your radar:

Assigning clear ownership of metrics to move and stakeholders of activities/ business areas as early as possible. A key DRI (direct responsible individual; whether PMM, VP, GM or other) is integral to successfully bringing cross-functional teams together, with a PMO a great aid in maintaining visibility and keeping things on track. (This can also fall to the DRI.)

Test, track, tweak. Experience is a great thing when doing launches, but whether you’re first to market or taking on a market leader, establishing your product/market fit, unique or resonating value props, customer advocates, and competitive advantages all need tracking, testing and tweaking.

Be mindful of internal readiness as far in advance as possible. Support, sales, customer success, internal operations, and more—if teams are not set up for success for inbound interest at launch, your road to revenue (and customer retention) is going to be a long one.

General priorities should align with business goals, whether:
- Driving revenue
- Increasing market share
- Establishing brand equity
- Successfully bringing an MVP to market to test product/market fit

Priorities should be clear before a GTM is created.

Excellent answers here. I agree that revenue is an important aspect of a Product Launch. You don't want the launch excitement to be short lived because of lack of revenue (and adoption). 

We wrote a blog post on this topic that you can refer to: What is your product marketing's "release to sales" process? 

In my opinion the three priorities for product launch are: 

• Start Early. This cannot be stressed enough. Apart from a product-market fit the next big thing that is working against you is time. You need to be smart about the launch and try to adopt some of the lean startup methods to test and revise your strtagey. 
• Define a Timeline. You need to be working against a timeline with clearly defined milestones. Obviously this timeline has to start way in advance before the actual product release by the engineering team. 
• Involve different stakeholders inside (and outside) the company. You cannot do this alone. You need the help of customer success, partners, existing customers, prospects and other constituents to help you maximize the impact of your launch.