- Play politics (a little bit)
It can't hurt to start to understand the politics or culture of the organization. Is this an Engineering-centric company, where Marketing is an afterthought? Or does the organization lead with Marketing? Is the Customer Success/Support function adequately staffed?
Reaching out to principals in Marketing, Engineering, Support, Operations, etc. will help you establish and reinforce your role. When interviewing these principals, you may hear sentiments ranging from, "Boy am I glad you're here!" to "Who are you again? (And why are you wasting my time?)"
Focusing your efforts on people who appreciate your role. You may have a broad charter or a narrow one; in either case, a quick win should be focused on teams that appreciate your presence.
- Know your role
What is the business case for your salary, and what have you been asked to do? Making sure that your wins align with the goals of the people who decided to hire you will reaffirm their decision and give you internal political capital. If you're a company's first-ever writer, why did your bosses decided writing needed to be one person's job, instead of a side task for several people?
- Triage
Seek out and embrace the triage process; your quick wins ought to be focused on "Severity 1 / Priority 1" issues. "Stopping the bleeding" is a quick win itself! Insist on attending bug triages (or backlog review, or any sort of formal prioritization process or bug scrub); doing so will quickly immerse you into the pain points of the product(s) and help you envision and prioritize first deliverables.
(Note that the highest source of pain may be customer-facing or internal. You may not necessarily have a charter to produce internal documentation, but if you are alleviating pain, you could make a case for producing something quickly for an internal audience. See above.)
- Hit the data
Can you pull data on the pain points and priorities listed above? If you're working on customer-facing content, what are your most-visited articles, which articles are most likely to lead to submitted help tickets and which common searches have low click-through rates for top results? Grab some data before you start working. After you're done, check how the data has changed. There's nothing like showing your supervisors that writing well can have quantifiable results.
- Use a "production values" strategy
Filmmakers use the term "production values" to prioritize those things which will end up in the frames of the final cut that viewers will see. For example, the dollars spent on catering to feed the cast and crew -- while important and necessary -- aren't actually seen in the end-product by the consumers of the film. Therefore, it may be wiser to spend more money on costumes or makeup rather than sandwiches. If your charter is to prioritize end-user-facing documentation, you may want to be brutally honest about those deliverables that will provide the largest value for your time invested.
- Don't be afraid to crow (a little)
Once you've done something great, let people know! As the writer, you have a clear understanding of the value of your work. Don't be shy about sharing that with your colleagues.