So you've been working on this product, got something interesting, probably even some customers, and a larger company got interested in the product enough to acquire the company (some of this advice also applies if they were interested in the people or something else other than the existing product, but I'm mostly writing here about the case where - at least supposedly - the intention is to keep and grow the product you were working on before the acquisition).
Some of the following is broken down by function but even more than usual this is a case where it pays to have some cross functional awareness of what is happening even if you are responsible for one of these areas more than others.
First of all, you are now part of a much bigger company. Therefore, a lot of the challenges are communication ones. There's a whole set of issues around getting to know people in disparate parts of the organization, setting expectations, self promotion, and probably a bunch I'm forgetting to call out specifically. But many of them change and get more important at a bigger company.
An acquisition tends to bring up a lot of feelings - for example excitement, accomplishment, sadness, and disorientation. Particularly for people managers, but also everyone, a lot of the job is talking people - including yourself - down from various ledges and getting information about benefits, offices (and/or remote practices), org charts, company strategy, and more. Basically to make sure people know what is going on, have input as feasible, and that things like 1:1s are doing the job of getting into issues which might be less amenable to blanket emails and the like.
For product, the key challenge is "are we working on what the higher ups acquired this product for?" But before even getting to that, regularly ask a more basic question: "Do people widely understand our product (existing and future functionality)?" The big company adage is "err on the side of overcommunicating" and my experience is that you need a lot of different ways to even get to a shared baseline of what we have today (for example, via demo days, screenshots, getting people internally to try the product, and bringing in customer input). Many of the same mechanisms also apply to a shared understanding of what we want to build next and why.
For technical issues, how does the other company handle deployment? Security? Programming languages? Testing? How much do we expect to standardize and how much do we expect to remain divergent? If we want to converge, what do we tackle first and how?
Culturally, the number one thing I'd focus on is how to have contact with people who had been from the other company. Maybe there are interest groups around hobbies, diversity, or charitable activities. Or more work-related things like "people using a common programming language", "people interested in security", or other concerns which may cut across the org chart. It can be easy to neglect things which aren't tied to a concrete deliverable, but the goal here is to build relationships. It is so much easier to navigate an unfamiliar organization and solve a tough problem if you know people and understand assumptions or typical ways of approaching things.
Will you stay with a company for long after acquisition? Does a product have a good change of thriving after acquisition? I'm not diving deeply into that, and there is no shame if the company you end up leaving in a few (months, years, whatever) just doesn't feel like the one you worked for pre-acquisition. But here I try to present the optimistic case for how you can jump into tackling a work situation which just changed (perhaps very dramatically) when your company was acquired.
