My suggestions are for aspiring PhD students in the life sciences but I suppose this may be applicable to other fields as well. While pursuing PhD in the States, I met and became friends with quite a few fellow graduate students who were couples before they even joined the program. It used to baffle me initially as to how they made sure to get into the same university for a PhD. And interestingly some of them did not have impressive test scores or research experience to get in.
After interacting with my couple friends for a while, I finally was able to understand how. When either one of them had better scores and was granted admission to PhD, they would typically start working in a lab and begin conducting research. At this time, their partner who did not apply yet or applied and did not get selected would start volunteering at a lab of their liking in the same university. Basically for about next 6 months to a year, the partner would help to conduct research for free at a lab of their interest. The main purpose of this volunteering process was to impress the professor enough so that they would go to the admissions committee and basically request that the student be granted admission into the PhD program, even if their profile is not outstanding. 95% of the time, the admissions committee would oblige. To be perfectly honest, most people that I observed volunteering manage to eventually get in. Basically the success rate of this trick is quite impressive.
Students are typically awarded funding and financial support in the PhD program for a limited time period, usually 5-6 years. If you are not able to defend your dissertation in that allotted time, you will most likely have to pay the university fee out of your own pocket and you may not even be entitled to a monthly stipend. In such a scenario, volunteering to learn and perform research at a lab of your liking helps you get an early handle on things and save precious time once you actually do get into the program. PhD students who straight away get admission into PhD and then start lab rotations, are investing the limited time they have into finding the right lab that is a good fit for their personality and research interests.
Another benefit of volunteering at an academic lab is that you get an opportunity to interact with graduate students, post-docs and professors at the university. This would serve as a wonderful opportunity to get some insider information about productive labs/PIs at the university of your interest by talking to people and also getting some first-hand experience yourself.
So if your girlfriend/boyfriend or spouse has gotten into a university for a PhD and you are trying to get into the same university and program, you now know what might be the best way forward..!