If you want to build general skills, we recommend that you start by adding ISTQB Agile Certification to round out your knowledge of Agile testing. It's the second most popular ISTQB certification among testers looking for jobs in the U.S.
Then we recommend that you choose from among these more advanced certifications, as they will prepare you for a promotion:
Test Analyst: This is designed for a tester who will have a deep understanding of the business domain and the needs of the user. Consider the Agile Technical Tester certification instead if your organization is all-in on Agile.
Technical Test Analyst: This is designed for the technically minded individual who has knowledge of programming or scripting.
Test Manager: This is designed for the tester who wants to lead and manage the QA process and other testers.
Specialized Testing Skills
If you want to build specialized software testing skills that set you apart, you will want a mix of several ISTQB specialty certifications based on your industry.
ASTQB's software testing career path does a great job of describing each of these options. We highly recommend that you review it once or twice per year because career options are added continually.
Regardless of which skills you choose next, keep moving forward! Technical people respect others with strong technical skills. Getting additional certifications shows you are staying current with software QA trends and are ready to take the next step up in your career.