A few tips:

Please contact your potential supervisor before the application, ideally weeks before the deadline and not the Friday before the Monday deadline.

Send your CV. Are you expecting to get a First or 2.1? I don’t care but the panels do!

Typos and bad grammar in emails or CV are usually not a good sign. Check them!

Why are you applying? Is it the group, the project, the city or what?

What is your long-term goal?

Look at the group’s papers. They tell you a lot about the type of research being done.

Don’t just look for groups where you think you can cure cancer (because you won’t). Look at the techniques you can learn there.

Is the supervisor someone you could work with? Speak to the current PhD students.

Is there post-doc support?

What happened to previous PhD students? Ask the supervisor! Where did they end up will tell you about the support and mentorship they have received.

And finally: if you are applying, check your emails regularly, respond on time and check your spam filter.